GOLDEN AGE:
This estimation depends greatly on what time period you are focusing on the city, the population would rise and fall due to various factors. According to Anthony Kaldellis, the conventional estimation in the mid 6th century peak of the population was around 500,000 people, but estimates range from 400,000-750,000 people! Intriguingly, he offers some insight on how these estimates are crafted by scholars. Kaldellis wrote that:
“Estimates are produced in three different ways: by guesswork; by correlating the size of the city with guesses about its population density, although it is not known how much of it was residential, and by calculating the number of people who could be fed by the shipments of Egyptian grain stipulated in Justinian’s Edict 13.8 of c.539. The last produces larger estimates, but assumes Justinian’s expectations were met and used only to feed Constantinople. Conventionally, half a million is understood as the high point in 541.” In short, he says these estimations are just a bunch of reasoned guesses from scholars with the limited information we have.
Paul Magdalino wrote about the population of Constantinople in the 6th century, estimating that the population of Constantinople was 300,000-500,000 . He, along with other scholars, believes the population declined in the following two centuries to a level possibly as low as 70,000 people. Other scholars like Robert Ousterhout also echo these population estimates.
URBAN DECLINE:
Magdalino details how the urban scale declined as the Roman Empire faced new levels of existential crisis:
“In the first half of the seventh century, Egypt was conquered temporarily by the Persians and then definitively by the Arabs, who thus deprived Constantinople of its main source of grain. In 626 the Avars cut the aqueduct. The empire’s finances, diminished by devastation and loss of territory, were consumed by the life-and-death struggle with these and other enemies. Contemporary sources do not record the impact on urban life, but the government was undoubtedly obliged to reduce the urban population, at least until local agricultural production was stepped up and dietary habits changed to allow for greater consumption of meat and fish. Almost no major new building or restoration project is reliably attested between 610 and 760. The main area of settlement seems to have contracted around the old Constantinian civic center and the harbor of Julian, the only port of entry and exit mentioned in sources of the seventh to tenth centuries. It was probably in this period of depopulation that burials began to take place within the Constantinian wall and that the monumental spaces on the edge of the civic center—the amphitheater on the Acropolis, the Strategion near the Golden Horn, and some of the fora along the Mese—began to be used as places of execution and markets for livestock. The great baths, theaters, and sculptured monuments of the fourth and fifth centuries fell into decay and came to be regarded as objects of superstitious dread from a legendary and exotic past. Even the upkeep of churches strained the available resources, and Frankish ambassadors in the mid-to-late eighth century returned with reports of basilicas that lacked proper lighting or even roofing.”
It is certain that over time the city did begin to shed people, and almost surely never hit 500,000 again. The Egyptian grain shipments which scholars used to estimate the population were lost in the 7th century. The Persians seized Egypt and the shipments halted around 619, though Egypt was briefly reconquered. After the Arab conquest in 642, Roman rule was permanently over in Egypt. The city population entered a downward spiral, and as scholars say, possibly plummeting to as low as 70,000 people. The aqueduct network also ceased function in the 7th century, which limited the upper ceiling of the population. Now, despite the huge decreases of this century, Constantinople was still bigger than any other contemporary cities in Medieval Europe. However, 70,000 inside a city which held at least half a million must have left many areas of urban ruins and cultivated land.
Robert G Ousterhout also wrote about the huge decline in population in the city: “If we are to view Constantinople as a city in transition, to my mind the most important urban transformation took place during the seventh to the ninth centuries. This period effectively marked its redefinition from a Late Antique to a medieval city. Constantinople had a population of perhaps 500,000 in the fifth century, which could have only been supported with a well-organized trading network that brought wheat from as far away as Egypt, and this also required sufficient ships, harbors, and warehouses. Elaborate works of engineering, like aqueducts and cisterns, were also necessary to provide and store water for the inhabitants. Without an elaborate system of trade and without quantities of water, a city of this size could not survive, and the population declined dramatically after the seventh century. Prior to the Arab siege of 717-18, Anastasius expelled all inhabitants who could not lay in a three-year supply of provisions. The population must have shrunk to perhaps one-tenth of its former size. The demise of trans-Mediterranean trade on an
Imperial Roman scale meant also that the medieval city remained small, with a large area of desabitato within the walls.”
I think this is a generalization, of course Constantinople did still have a water system. It did fall into disrepair at this time, indicating a far lower population, but it was also brought back into function later when needed. Cisterns were of course present, and without the aqueduct they were the main source of water for the city.
The decline in Constantinople continued after the Arab siege as well, peaking with a large outbreak of plague in 746. The Emperor Constantine V replaced the population of the city with Romans from Greece and islands of the Aegean. A couple decades later, he stepped up his repopulation efforts and repaired the Aqueduct of Valens, which had not operated in 140 years. This was the turning point for the city of Constantinople to be reborn as a giant metropolis once again, growing until 1204 when the fate of the city suffered its infamous and tragic fate.
RECOVERY:
During the decline periods the city had contracted to the southern area, but the reviving city began to grow outwards, and in the 11th century the Golden Horn and Blachernae really took off in terms of growth. Emperor Alexios Komnenos moved the imperial residence to Blachernae, which naturally encouraged growth there, and of course in the areas between the Great Palace and Blachernae.
After bottoming out as the Empire nearly collapsed in the face of the Arab threat, Constantinople sort of reflected the situation of the Roman Empire. As the Empire stabilized and recovered, so did the Queen of Cities. The growth was more gradual, though it seems it accelerated in the 11th century. The population is cited as being as high as 400,000 as per Geoffrey Villehardouin, who thoroughly destroyed the city with the Fourth Crusaders in 1204. Anthony Kaldellis says it seems high, but does not specifically refute the number or offer an alternative. So it seems 300-400,000 is a reasonable estimate for the 12th century second peak of Constantinople.
Magadalino described the population of the city as it peaked in the 12th and early 13th centuries: “The population of Constantinople, including merchants, litigants, and other transients, may have numbered as much as four hundred thousand in 1204 and occupied a built-up area corresponding very closely to that of the sixth-century city, with a dense concentration around the commercial district and tentacles of development along the seashores and the branches of the Mese leading to secondary nuclei in the northwest and southwest corners. The settlement used and reused the buildings of the late antique, early Christian, and earlier medieval phases in ways that ranged from careful conservation through structural conversion to outright quarrying. Whether the result was a pleasing blend or an incongruous jumble is impossible to say, but no part of the city was entirely a recent creation, and Constantinople was probably more closely, richly, and naturally in touch with its physical origins than any other city surviving from Greco-Roman antiquity.”
LATER BYZANTINE ERA:
The Fourth Crusade shattered the fabric of the Empire, and Constantinople in an irreversible and tragic way. The city population severely declined, as did its material wealth. It possibly went as low as 30,000 people. When the Romans liberated Constantinople in 1261, the city did rebound slightly but the Romans did not possess the resources necessary to truly rebuild and restore the city to its former splendor. Anthony Kaldellis says in the early 15th century there were around 70,000 people while in 1453 the population was possibly as low as 25,000.
The population was so low in later centuries for a city designed to be large enough to hold 500,000, that it left large empty areas. A visitor named Clavijo, the ambassador of Spain to the Timurid court, stopped in Constantinople in 1403 where he was able to get a personal tour with the son in-law of the Emperor because he claimed they were distant relatives. Nike Koutrakou says that “Clavijo’s descriptions focus on churches and monasteries; however, he also notes the ubiquitous existence of ruins and vegetable gardens inside the walls, confirming the fifteenth-century city’s decay.”
SOURCES:
The Cambridge Companion to Constantinople, Chapter 5: The People of Constantinople by Anthony Kaldellis
Medieval Constantinople: Built Environment and Urban Development. Paul Magdalino
Building Medieval Constantinople, Ousterhout, R. G. (1996)
The Conquest of Constantinople, Robert De Clari
shadowsofconstantinople.com 