Source Data Reference for:

City = Cologne
Time = 1000

City	Year	Size	Size Comment	Year Comment	Author	Title	Location
Cologne	900	21,000			Paul Bairoch	La population des villes europeennes de 800 a 1850
Cologne	1000	21,000			Paul Bairoch	La population des villes europeennes de 800 a 1850
Cologne	1000	21,000			Tertius Chandler	Four thousand years of urban growth	p538
Cologne	1000	21,000			Tertius Chandler	Four thousand years of urban growth	p15