London through the ages

A video available here shows the development of London since Roman times, with emphasis on the structures that have been preserved.

The yellow dots show Roman archaeological sites. In
Roman times the population may have reached 30,000

After the Romans left, Anglo-Saxons settled in farmsteads
 and, by the 9th century, within the Roman walls

In the prosperity of Tudor times, by 1600 the population rose
to about 200,000 

 Many Tudor and early-Stuart structures were lost in the Great Fire of 1666, and more during the slum clearances of the 20th century. And of course structures of all ages were lost in bombing during WW2.

By 1840 the population was 2 million - the largest city in the world. 

As the chief city of the British Empire, Victorian London had 6 million inhabitants.
Between the 1940s and 1970s, many Victorian buildings were lost to commercial development