What were the largest medieval cities?

Answer 1

There was a huge variation in the sizes of cities during the Middle Ages.

Rome, which had a population as high as 1,000,000 during the Empire, fell to 30,000 early in the Early Middle Ages and recovered somewhat only to lose many people during the Black Death.

Constantinople is estimated to have had about 500,000 in 600 AD, but Plague of Justinian and the loss of grain shipments from Egypt reduced the population to about 40,000 to 70,000 in 800. In the the 9th and 10th centuries it recovered to about 500,000 to 800,000, but by the 15th century had again reduced to perhaps 65,000.

London had a population of 10,000 to 12,000 in the Early Middle Ages. This was increased to about 18,000 in the time of the Norman Invasion. By 1300, it was increased to 100,000, but it was again reduced to 65,000 by the Black Death.

Paris had a population of about 200,000 in 1347. It was hit very hard by the Black Death.

Cordoba had a population estimated at about 400,000 in 1000 AD, though the range of estimates is from 250,000 to 1,000,000. It was considered the most culturally advanced city in Europe at the time.

There were a number of other large cities, but as one might see, comparing them meaningfully is difficult.