In the tenth century, what was the largest city in Western Europe?

Cordoba Spain

https://en.wikipedia.org/wiki/C%C3%B3rdoba,_Spain

From modest beginnings in the 10th century BC, Rome became the largest city of the ancient world and the center of the Roman empire. Tradition records a series of kings of Rome until 509 BC when the Roman republic was established. Relatively little is known archeologically about the city in the regal and earlier republican periods; the extensive remains now visible date mainly to the later republic and empire.

The city was embellished by the great patrician families and emperors, with forums, temples, theaters and circuses. As Rome's population grew, so did its infrastructure of roads, aqueducts and warehouses. Its political importance declined in the 3rd century AD as it was abandoned by the emperors for centers closer to the embattled frontiers.

http://www.orthodoxengland.org.uk/pdf/euspiritcap.pdf

This site suggests Cordoba:

The 10th century Caliphate of Córdoba was the largest, culturally the most sophisticated polity in all Europe. Contemporary chroniclers, all of them Arabic, like the geographer Ibn Hawkal in 948, marvelled, "The amount of coins in circulation! The variety of crops grown! The people! "The textiles! The gardens! The mosques!" — There were more than 600 mosques and 900 public baths, 50 hospitals and several large markets. "You could walk through her streets for ten miles in one direction at night, and always have the light of lamps to guide your way. Seven hundred years later this would still be an innovation in London or Paris, as would pave streets." It is believed that Córdoba was the largest city in the world from 935 to 1013.

http://www.spaniasidene.com/eng/spain_area_%20information_spanish_cordoba_andalucia_city_costablanca_costadelsol_spain.htm

Quite a few sites say Cordoba:

This AM we start on tour of Cordoba, which in the 10th century was the largest city in Western Europe and is now a UNESCO World Heritage site.
http://www.greatrailuk.com/holiday.asp?holiday=597

It has been estimated that Cordoba, with up to 500,000 inhabitants in the tenth century, was the largest city in Western Europe and, perhaps, in the world.
thepolitic.com/archives/2008/01/13/islamic-reconquest-in-spain no longer exists

While the rest of Europe was languishing during the “Dark Ages”, Cordoba thrived and, in the 10th and early 11th centuries, was the largest city in Western Europe; a period characterized by remarkable success in trade and culture.
http://www.madridandbeyond.com/special/citytours.asp

In fact Cordoba was the Muslim capital of the Iberian Peninsula and the largest city in Western Europe in the 10th century.
http://www.koppelquests.net/Spain%20Pages/November_4.htm