by Tony Brown
The IPCC AR4 projected sea level rise in 2100 to range from 18-59 cm, depending on the emission scenario. More recent projections are for a 1 m sea level rise in 2100 [here and here]. Apart from the issue of uncertainty and reliability of these future sea level projections, how do these magnitudes of sea level rise compare with historic variations in sea level rise?
Historic variations in sea levels is in three parts. Part 1 covers the Holocene to Roman times. Part 2 traces sea level changes to the Medieval Warm Period. Part 3-the modern age from 1700 to today.
This post is an abridged version of a longer document (Part 1), replete with references and additional diagrams and pictures.
The IPCC on historic sea level rise
The IPCC AR4 statement on historic sea level rise from AD0 is cited below:
“Yes, there is strong evidence that global sea level gradually rose in the 20th century and is currently rising at an increased rate, after a period of little change between AD 0 and AD 1900. Sea level is projected to rise at an even greater rate in this century.
The two major causes of global sea level rise are thermal expansion of the oceans (water expands as it warms) and the loss of land-based ice due to increased melting…
Global sea level rose by about 120 m during the several millennia that followed the end of the last ice age (approximately 21,000 years ago), and stabilised between 3,000 and 2,000 years ago. Sea level indicators suggest that global sea level did not change significantly from then until the late 19th century. The instrumental record of modern sea level change shows evidence for onset of sea level rise during the 19th century. Estimates for the 20th century show that global average sea level rose at a rate of about 1.7 mm yr–1.”
The IPCC provides no references for this FAQ on “Is sea level rising?”
The Figure below from the Wikimedia Commons shows sea level rise since the end of the last glacial episode. Because of the large magnitude of the change, the scale on the y-axis makes it impossible to resolve the magnitude of changes for the last 8,000 years. An expansion of this diagram for the past 9000 years enables examination of the sea level rise on the scale of meters. The uncertainty of the estimates at individual locations plus the range across different locations at any particular time can be associated with an uncertainty of several meters, which is larger than the magnitude of projected sea level rise that is under consideration.
Challenges in reconstructing and interpreting historical sea levels
Apart from the uncertainties in actually determining sea level change, the physical interpretation of sea level change needs to take into account deposition and erosion, land movement-often through post glacial rebound- and tectonic activity, in addition to climate change.
These historic changes in land level-dramatic or gradual- will have been taken into account in academic studies (although there is not unanimity over the rate of change). However all these factors demonstrate that accurate sea level reconstruction is problematic.
In private email correspondence that he has given me permission to reproduce, Dr Simon Holgate of Proudman Oceanographic Observatory refers to sea level reconstructions back to 200AD-which covers several warm periods such as the Roman Optimum and MWP- and remarks:
“It seems plausible that sea level would be higher in a warmer period (how warm and how much of the Earth was actually affected by the warm period is debated) but it isn’t clear how sea level would respond. So maybe it was higher than today, or maybe it wasn’t. We have no observations and we just don’t know. For me, there is far too much uncertainty in the ‘reconstructions’ of sea level for them to be very useful…Overall I would say that the evidence from the (Roman) fish tanks etc suggests that there has been no real change in the average height of sea level over the last c. 2000 years prior to the mid to late 1800s.”
It is important to fix in our minds therefore that sea level change is not necessarily as a result of their being less or more water (through glacier melt and thermal expansion) but that much of what we might observe is as a result of changes in the height of the land relative to the sea.
Doggerland
We commence our watery journey with this short excerpt from the book ‘The Little Ice Age’ by Brian Fagan, Professor of Archaeology at the University of California.
“Ten thousand years ago the southern North Sea was a marshy plain where elk and deer wandered…England was part of the continent until as recently as 6000 BC when rising sea levels caused by post ice age warming filled the North sea.”
“Prof. Bryony Coles has been examining the archaeology of “Doggerland”, which now lies under the North Sea. Its highest point is the submerged Dogger Bank where prehistoric artefacts are occasionally found by fishermen and geologists. At the height of the last Ice Age, Doggerland was dry and stretched from the present east coast of Britain and the present coasts of The Netherlands, Denmark and North Germany. Thus, the so-called land-bridge, was a place where people settled as the ice-sheets wasted and north Western Europe became habitable once more. But, as the ice-sheets retreated further and sea levels rose, the North Sea encroached on the land, eventually separating the British Peninsula from the mainland.”
It is a sobering thought that where once our ancestors hunted, fish now take their place, and graphically illustrates that sea level rise is by no means a modern phenomenon in the context of human history.
St. Michaels Mount
Let us now move from Doggerland on the east coast of Britain, through several thousand years to the Roman period on the Western coast of Britain. Where better to examine sea level fluctuations than a place especially susceptible to them -a tidal island known as St Michaels Mount in Cornwall.
From the Wikipedia:
“St Michael’s Mount (Cornish: Karrek Loos y’n Koos) is a tidal island located 366 m (400 yd) off the Mount’s Bay coast of Cornwall, United Kingdom. It is a civil parish and is united with the town of Marazion by a man-made causeway of granite setts, passable between mid-tide and low water. The island exhibits a combination of slate and granite. Its Cornish language name — literally, “the grey rock in the wood” — may represent a folk memory of a time before Mount’s Bay was flooded. Remains of trees have been seen at low tides following storms on the beach at Perranuthnoe, but radiocarbon dating established the submerging of the hazel wood at about 1700 BC.
The ancient Cornish name for the mount certainly suggests it was once dry wooded land. In his ‘Report on Cornwall’, Sir Henry de la Beche remarked that:
‘Submarine forests are so common that it is difficult not to find traces of them in the district at the mouths of all the numerous valleys which open upon the sea and are in any manner silted up’.
The folk memory of woods and a rock is supported by modern observational evidence which confirms that the woods existed, with radio carbon dating suggesting they were submerged around 1700BC.
Sir Gavin de Beer, F.R.S., a former Director of the Natural History Museum, wrote in his book Reflections of A Darwinian, published in 1962, that scientific methods of analysing the traces of old tree trunks still found in Mount’s Bay had indicated that the forest was submerged by the sea at least 1,500 years before Pytheas came there on his voyage of exploration in about 325 B.C
Modern science does not confirm precise dating, but the legend talks of a Kingdom stretching from Penwith in Cornwall to the Scilly isles. Page 3 of this study from 2006 seems to confirm a series of inundations, suggesting some truth in the older legends, and that the earlier Romans-or their predecessors- may have viewed the Scillies as one land mass rather than the series of islands it has subsequently become:
“From the beginning of the Holocene period, as the ice sheets melted and sea level rose, the submergence of low-lying areas led to the formation of one main island by about 3,000 BC. This included the present islands of St Mary’s, Bryher, St Martin’s, Tresco, Samson and the Eastern Isles, with three smaller tracts of land around St Agnes, Annet and the Western Rocks (Ratcliffe and Johns 2003, 4). Charles Thomas’ model for sea level change in Scilly suggests that at around 1000 BC Mean Sea Level (MSL) was 7.25m lower than today, with the modern 5m marine contour roughly representing the coastline at that time (Thomas 1985, 17–64). The main island may have survived until the end of the Roman period but further rises in sea level, and perhaps a final inundation during the early second millennium AD, resulted in the eventual submergence of the ‘flats’ in the middle of the land mass and formation of the present pattern of islands. Final separation of the islands might not have been complete until the early sixteenth century.”
Interestingly, this last account places the inundation at around the period that Lyonesse was said to be drowned- around 3000BC.
It is said (by the local tourist board) that King Arthur’s castle is located at nearby Tintagel on the North Cornish coast. So the area-whether or not as part of some legendary Arthurian Kingdom-was undoubtedly inundated by rising sea levels, and here we can find some definitive scientific information about the subsequent rise to prominence of St Michaels Mount, following its transition from an inland place in a forest to a port.
So to summarise, over historic- rather than geological time, St Michaels Mount- which was originally some distance from the sea -became flooded following several periods of dramatic sea level rise. The first during the Doggerland era and then also at some point around 3000 BC or so, of which the folk memory of Lyonesse still lingers, and possibly again 1000 years later. Whether the levels fell in the interim period is outside the scope of this study, but we do know that by 350BC at the latest St Michaels Mount was a thriving port for the export of tin, which during the ebb tide was carried over in wagons i.e. by that time it was a tidal island.
To put in context that sea level fluctuations are often about the characteristics of land rise or fall, we refer again to the earlier study (original article here) from Durham University. According to this academic study, Cornwall, together with the adjacent counties of Devon and Somerset, is one of those areas of falling land which (apart from any other reasons such as thermal expansion and glacial melting) is thereby causing rising sea levels. The land is falling at 0.5mm/yr which comes to some 1 meter over 2000 years.
In a personal email to the author Simon Holgate of Proudman Observatory amplified this study:
“With respect to Newlyn, (close to St Michaels Mount) it is probably the highest quality tide gauge record in the world. The land is the region is subsiding by about 1 mm per year due to the effects of the last glaciation. You can see the data for yourself here. Once we’ve taken the “glacial isostatic adjustment” into account we’re left with about 1.4 mm/yr, which is typical of Europe and slightly less than the global average of 1.8 mm/yr over that time period.”
So taking this into account we should reasonably assume that the sea level we see now is going to be around 1 meter greater than was current in 350BC for reasons of the land sinking and quite apart from any genuine sea level rise. Is that increase verified by the observations we can make?
No. Today St Michaels Mount is still not navigable for large parts of the tidal cycle as was also observed in historic times. There are better places nearby to have acted as a historic tin port, for the Mount is dangerous when the wind is from the wrong direction.
St Michaels Mount remains a tidal island today, although the studies seem to indicate that after 2000 years it should now be surrounded by sea at all stages of the tide due to land movement alone-irrespective of the notion of modern sea level rise. The tide window today for a fairly deep draught ship who had travelled some distance and who would be unwilling to hove to in treacherous waters is still fairly small-a matter of a few hours in each tidal cycle.
If the port was bustling 2000 years ago it is reasonable to suppose that tidal access was less limited then than it is today-or was at least as good. Consequently the evidence suggests that in 350BC there was probably a little more water than exists today in order for it to be a worthwhile place to ship cargo from, and therefore current ocean volume (glacier melt and thermal expansion) is less now than then, to take into account the known land changes. There was speculation that in Phoenician times the island was still connected to the mainland by a spine of land (Bloch et al) but that can not be authenticated by recent archaeological evidence, and as other accounts clearly describe it as a tidal island.
A broader perspective on historic sea level changes in the UK
Thus far we have concentrated on one small part of one small country, albeit the tidal island is an interesting proxy. Britain, as one of the world’s largest islands, is a good place to examine sea level changes, helped by the wealth of visual evidence and written records created through a long period of continual habitation. At this stage of the study, therefore we will look elsewhere in the UK for evidence of likely sea levels in the Roman period. Specific examples are provided below
From this article:
“ In Northumberland, researchers found sediments from 7,000 years ago five metres below, and others from 4,000 years ago at 1 metre above the present sea level. This indicates that the sea level rose above present levels from around 7,500 years ago to 4,500 years ago, and then dropped and is continuing to fall. Sea-levels in most of Scotland peaked even higher about 4,500 years ago and have been falling ever since because the land has risen.”
To put these changes into a human perspective, the remains of a drowned Mesolithic village was found on what is now the sea bed off the Isle of Wight on Britain’s South coast. [link]
“A few Archaeologists originally found Mesolithic flint tools within a 1km stretch of seabed over a decade ago. This was the first time such pieces were found in their original location underwater around the British coast. Ten years on, continued searching has recently resulted in much more startling finds. Elements of a substantial wooden structure ( found in 2009) built about 8,000 years ago by our Mesolithic ancestors. Some of the recovered timbers have very clear, distinct and sophisticated cut marks, so we know they have been worked on by humans capable of craftsmanship. These could be part of a collapsed structure, or perhaps a platform built close to a waterway.”
According to the BBC ‘Britain’s Drowned World’ TV programme carried out by ‘Time Team’, the inundation was caused by a prolonged sea level rise at 2cm per year (around 10 times the current rate) and exacerbated over a 15 year period by a 7 degree Fahrenheit temperature rise.
A discovery of a fort formerly on te shore is discussed here:
Pevensey in Sussex (South Eastern Coast) was one of the ‘forts of the Saxon shore’-built by the Romans in the 3rd century to keep out the Saxon invaders. The castle -still visible-now lies a mile or two inland but was very important at the time of the Romans.
The need for this fort is graphically described here:
“The North Sea had a nasty little jump between 350 and 550AD, flooding the coasts of northern Europe with an extra 2 feet of water and sending its inhabitants — folk known as Angles and Saxons — fleeing (although “conquering” might be the better word) into ill-prepared Roman territories. At the start of this rise, the areas we know as the Fens were a well-settled part of Roman Britain ruled from the town of Duroliponte (Cambridge) by its native people, the Christianized Romano-Celtic Iceni. Then the sea level rose, and history’s curtain went down for two centuries.”
The Roman castle evolved into a Saxon fort and then a medieval castle. When it was built it commanded the entrance to a harbour and was surrounded by the sea on three sides. [link]
Thanet, on the South East coast of England, yields further evidence:
“Rectangular and curvilinear enclosures have been recorded at Dumpton Gap and Broadstairs on the east coast of the island (both of which may indicate small subsistence farming communities) whose incomes were bolstered by the extraction of salt from sea-water, as evidence linked to this activity has been found at both of these sites. The industry was probably curtailed by the early 3rd century at these sites, however, due to the rising sea-levels. Burials have also been recorded at both sites.”
“At Faxfleet a Roman site was probably abandoned in the 4th century AD as a result of rising sea levels.”
“A Roman road was built northwards from South Ferriby towards the Humber during the 1st and 2nd century ad but this became buried by estuarine sediment within around 200 years of its construction indicating rising sea levels” (also see further references on Page 114 of this link)
This next item refers to an academic studymade to the east of London:
“These indicate a sequence of oscillations of relative sea levels to land mass as the sea has advanced and regressed over the last 10,000 years. The mean relative sea level curve shows an overall trend of a steadily rising sea level with time (see Devoy 1977: 714 fig 2) with levels in our period of +0.4m above present (OD) (Newlyn). For our period the Thames IV transgression phase equates to the middle of the third century AD (c 1750 yr bp), when sea levels at Tilbury were approximately +0.4m above present OD ordnance datum (Newlyn) (Devoy 1977; D’Olier 1972: 127).”
And finally, from this article:
“There appears to have been a general abandonment of settlements across the region during the late Roman Iron Age and the Migration period, probably due to rising sea-levels and storm-tides in the 4th century. Settlement recommences in the 7th or 8th centuries, often in areas that had been previously favoured as settlements sites in the Roman Iron Age.
Historical sea level references from elsewhere in the Northern Hemisphere
Still in the Roman era we now travel further afield to ascertain the characteristics of sea levels in other countries.
The first study is by Lambeck et al. in the scientific journal (Earth and Planetary Science Letters) entitled “Sea level change from Roman times in Mediterranean,” which illustrates some of the complexities of this subject:
“Here, we present results for sea-level change in the central Mediterranean basin for the Roman Period using new archaeological evidence. These data provide a precise measure of local sea level of -1.35±0.07 m at 2000 years ago. Part of this change is the result of ongoing glacio-hydro isostatic adjustment of the crust subsequent to the last deglaciation. When corrected for this, using geologically constrained model predictions, the change in eustatic sea level since the Roman Period is -0.13±0.09 m.”
From a second study by the same author:
“During the detailed excavations of ancient Caesarea, Israel, East Mediterranean, 64 coastal water wells have been examined that date from the early Roman period (with the oldest occurring in the 1st century AD), up to the end of the Crusader period (mid-13th century AD). The depths of these coastal water wells establish the position of the ancient water table and therefore the position of sea level for the first century AD up to 1300 AD. The connection between the coastal water table and changes in sea level has been established from modern observations in several wells on time scales of days and months and this is used to reconstruct sea level during historical time. The results indicate that during the Byzantine period, sea level at Caesarea was higher by about 30 cm than today. The Late Moslem and Crusader data shows greater fluctuations but the data sets are also much smaller than for the earlier periods.”
This next study is of a Roman market:
“After rapid submersion of the Roman market, crustal uplift explains the death of the marine organisms. These radiocarbon dates are compatible with epigraphic data, which mention the Roman market for the last time in A.D. 394. This implies a rapid relative sea-level rise during the fourth century A.D.”
“.. According to the new data, submersion of Pozzuoli was not a unique event, but included three maximum threshold oscillations between the fifth and fifteenth centuries A.D. (1) During the first phase, marine transgression of the Roman market ended ca. A.D. 400–530 after its last restoration in A.D. 394.”
This of an earlier Egyptian harbour;
“Archaeological investigations along a carbonate / conglomerate terrace located 600 m landward of the Red Sea coast in Egypt have uncovered the existence of an ancient (~4 kya) Egyptian harbor, a site from which seafaring ships departed for trade routes along the African Red Sea coast. Nearly 10 years of excavations at Mersa / Wadi Gawasis, a Middle Kingdom Egyptian site, have documented evidence for occupation on the top and at the base of the terrace, including temporary shelters, rock-cut caves, ceremonial structures, and industrial areas for metal working.
Ground penetrating radar, sediment coring, malacological and foraminiferal studies, radiocarbon dates, and rheological models demonstrate that the wadi bed adjacent to the terrace was once an open, protected bay. The base of the corraline / conglomerate terrace consists of a narrow coral-beach rock platform (dated at ~3500 BP) presently buried by anthropogenic, eolian, and colluvial sediments. Ubiquitous medium-fine wadi sediments underlie and extend beyond the beach rock. Malachological analyses, foraminifera distributions, radiocarbon dates, and sedimentological data indicate that these sediments were deposited in a protected tidal lagoon receiving infrequent freshwater inputs. Wave-cut notches along the seaward shoreline confirm a site-specific rheological model for the northern the Red Sea that indicates a sea-level highstand (~1 m above present MHW) during or immediately prior to occupation. Late during the period of occupation, the lagoon began to close as equatorial siphoning forced a regional sea-level fall while at the same time, riverine discharge through the wadi processes were infilling the bay at rates on the order of .25 cm/year.”
Some details on Ostia Antica from the Wikipedia:
“Ostia Antica is a large archeological site, close to the modern town of Ostia, that was the location of the harbour city of ancient Rome, which is approximately 30 kilometres (19 mi) to the northeast. “Ostia” in Latin means “mouth”. At the mouth of the River Tiber, Ostia was Rome’s seaport, but, due to silting and a drop in sea level, the site now lies 3 kilometres (2 mi) from the sea.[1] The site is noted for the excellent preservation of its ancient buildings, magnificent frescoes and impressive mosaics.”
The following references are provided from this site covering our period of study are from the Middle East, Holland, Britain, Greece, Egypt, and Germany.
“In the ancient port Caesarea, south of Haifa, stands a wall which must have been built between the time of Herod and the 2nd century. (A. Negev , personal communication , 1962). The top of this wall, now 1.50 m above the present sea level, is perforated with the typical holes made by the Lithophaga. The wall stands vertical and shows no sign of tilting. Near this wall are the remains of two aqueducts which once supplied Caesarea with water. Of the two, the older one was built near the present shore line; the parallel and newer aquaduct, situated further inland, must have been constructed when the sea was threatening and ultimately destroying the first one (REIFENBERG, 1951, pp. 27-28). It is most probable that the original aqueduct was constructed during Herod’s reign or shortly after, and that it was situated at that time quite far inland. It is estimated that it was destroyed towards the middle of the first millennium A.D. and the sea, therefore, must have been temporarily 1-2 m higher than it is now ((Fig.4C) “.
“Not only are the aquaducts of Caesaria (REIFENBERG, 1951) and the columns at Puteoli still in the original positions of construction (two things which would be almost impossible if there had been a tectonic movements of 3 m vertical amplitude since their erection) but many other old buildings in the reputedly unstable Mediterranean area are still vertical, a sign that the instability in many places was not great enough to cause a tilt. At the old shore the Etang of Vendres, near the mouth of the Aude, are the ruins of a Roman Therme of the 1st or 2nd century A.D. (locally called the temple of Venus). There the walls have been washed out by waves so that they now have a deep double notch about 1.80 m above present sea level (Fig. 4C). The remaining walls of the “temple” are not tilted at all.”
“Unfortunately these methods can only give estimates of within time intervals of several hundred years and differences of heights of half metres at best. Still, it is clear that the sea level at the Frisian coast according to 14C peat determination was higher ((Fig. 4C) in the middle of the first millennium A.D. than it is today and much higher than it was in the first millennium B.C. (Fig. 4F). The maximum in the middle of the first millennium A.D. is also supported by 14C data in the stable Recife area of Brazil (VAN ANDEL and LABOREL, 1964) (Fig. 4D).”
“Similarly the studies of GODWIN (1943), (archaeological , palynological and ecological) show for the middle of the first millennium A.D. (Fig. 4C) a definite rise of 1 m in the Fenlands of East Anglia over the present day sea level there, and a subsequent fall of several metres below today’s level in the 11th century A.D. (Fig. 4B).”
“Between 1200 and 7 B.C. (Fig. 4C) we have evidence of an high sea level: Ramses II succeeded in connecting the Niles to the Red Sea by a canal (1200 B.C.) (Fig. 4G) (MUIR, 1924) which re-used later by Trajan and still later by the Arabs, as mentioned before (650 A.D.) (Fig. 4C).”
“In Schleswig (Haitabu area) a cutba river is indicative of a sudden rise of the sea level (1000 B.C.) (Fig. 4G) (K(STER, 1960).”
Alternate interpretations
From the above analysis, there appears to be solid evidence that, after taking land changes into account, sea levels in Roman times were rather higher than today, as measured in a variety of locations. At this point any author after having proven their hypothesis (to their own satisfaction) would be wise to quit whilst they’re ahead and not face up to contradictory information. However that would lead to a charge of cherry picking, so it must be said that my assertions to date seem to be refuted by this 2010 article that comes from much the same part of the world as earlier studies. It appeared in a variety of places including Science Daily.
Science Daily featured a mix of selected quotes from the press release of a new study on sea levels, with which they combine into their own narrative. Some excerpts:
“The sea level in Israel has been rising and falling over the past 2,500 years, with a one-meter difference between the highest and lowest levels, most of the time below the present-day level.
“These revealed that the sea level during the Crusader period — just 800 years ago — was some 50-90 centimeters lower than the present sea level. Findings from the same period at Caesarea and Atlit reinforced this conclusion. When additional sites were examined from periods before and after the Crusader period, it was revealed that there have been significant fluctuations in sea level: During the Hellenistic period, the sea level was about 1.6 meters lower than its present level; during the Roman era the level was almost similar to today’s; the level began to drop again during the ancient Muslim period, and continued dropping to reach the same level as it was during the Crusader period; but within about 500 years it rose again, and reached some 25 centimeters lower than today’s level at the beginning of the 18th century.”
So the conclusion would be reached from reading the article that although the sea level was almost as high as today in Roman times it subsequently dropped, rose again to some 25cm, lower than today and as we all ‘know’ has surged to new levels in the last century.
The original study is found here. It appears that inexplicably a significant portion of this study was omitted, which throws a rather different light on the Science Daily story. The original study states:
“The Caesarea results indicate that about 2000 years BP sea levels was at its present elevation, (note; not ‘almost similar to today’s) while during the Byzantine period it was at or above its present level by (about 30cm- plus or minus 15cm) During the Crusader period “(around 1300AD)”sea level may have been lower than today by about 40cm, plus or minus 15cm.”
That the Science Daily version can have a rather different inference than the study and that some key parts have been omitted can be seen in the attribution by SD; The above story is reprinted (with editorial adaptations by ScienceDaily staff) from materials provided by University of Haifa. (Their link then originally lead to the University’s home page in Hebrew)
Let Dr Sivan himself have the last word which can put the Science Daily reporting of this section into its proper context now we know the complete story:
“Over the past century, we have witnessed the sea level in Israel fluctuating with almost 19 centimeters between the highest and lowest levels. Over the past 50 years Israel’s mean sea level rise is 5.5 centimeters, but there have also been periods when it rose by 10 centimeters over 10 years. That said, even acute ups and downs over short periods do not testify to long-term trends. An observation of the sea levels over hundreds and thousands of years shows that what seems a phenomenon today is as a matter of fact “nothing new under the sun,” Dr. Sivan concludes.
This observation is interesting as the use of the word ‘fluctuating’ can be matched to an earlier reference in other studies to ‘oscillating’ whereby is implied that over the last few thousand years or so sea levels have moved up and down around a central average by up to 30 cm or so.
Summary: Part I
So notwithstanding the statements of the IPCC AR4 who assert a sea level status quo from ancient until modern times, there are many studies that point to a picture of relatively static sea levels after the initial Holocene rise. These then show that some 3000 years ago there was a further inundation (think Lyonesse in Cornwall) and in early Roman times levels were somewhere around current levels. Levels then rose significantly through the Roman period peaking around the 700 AD Byzantine period at levels higher than today, which concludes at this period of study for Part 1.