2/ Let's start in the beginning.
London is an ancient city dating back 2000 years. The Romans founded the first recorded settlements around 47 AD. The Roman conquest lasted until around the 5th century, and various Roman ruins can still be found in the city.
https://en.wikipedia.org/wiki/Londinium
https://www.timeout.com/london/things-to-do/where-to-find-londons-secret-roman-sites
3/ In 1066 the Normans conquered England, and then decided to take an inventory. The result was the Domesday Book, a comprehensive survey of the country, including around London.
https://en.wikipedia.org/wiki/Domesday_Book
Back in 2012 Anna Powell-Smith presented "Open Domesday" at Geomob London - a project to overlay the survey results on a modern map: https://opendomesday.org
#geomobLON