Old Sarum was the original site of the cathedral city of Sailsbury, that began life in around 400 BC as a vast Celtic Iron-Age fort.

Following the Norman Conquest, William the Conqueror created an inner motte and castle, transforming it into a nigh-impregnable fortress, with its own city and cathedral.

However, Old Sarum was not a good site for a city, and after the clergy demanded the cathedral moved to the site of New Sarum (modern Sailsbury) the site was eventually abandoned to become a rotten borough, until 1832, when the Reform Act was passed.

Location

https://www.google.com/maps/d/u/0/viewer?mid=zeFjKTSyb0Bg.k-Twczr5u4bM&hl=en

Sources:

A booklet from the English Heritage

http://basementgeographer.com/old-sarum-and-rotten-boroughs/

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