The English Civil War had a tremendous physical impact on Bristol.
When war broke out in 1642, Bristol was seen as a potentially attractive stronghold by both sides. Although Bristol tried to stay neutral, Parliamentary troops faced little resistance when they took the city in 1642.
Bristol's medieval defences were both inadequate for its size and unable to withstand cannon fire from the surrounding hills so the Parliamentarians began a massive programme of works to create an outer line of forts, walls, ditches and ramparts. Bristolians paid for most of this work, but those who could not afford to pay had to physically work on the construction.
Sir Bernard de Gomme, a military engineer observed
"The city of Bristol stands in a hole & upon the north side towards Durdham downe, be 3 eminenter knolls or rockye hills, now crowned with so many forts."
The works were put to the test in July 1643, when two Royalist armies converged on Bristol. The outer works were from finished (particularly where rocky ground had made digging difficult) but the inner ring remained solid. Nevertheless Bristol was surrendered to the Royalists and its defences were then further strengthened with buildings like the Royal Fort (designed by de Gomme). This was the headquarters of Prince Rupert's army until it was taken by Cromwell in 1645.