Then, in the 1860s, there was a flood of newcomers for yet another reason. Between 1860 and 1880, the City of London was violently rebuilt. New sewers, railways and roads, made life unbearable for those living in the city and destroyed hundreds of dwellings, especially among the slum rookeries of the poor. Often major street corners, with their better quality buildings, were left and new roads cut diagonally through the centres of terraces, destroying many of the inner courts and mews where poorer people had huddled. No new housing was offered to those ejected, so they had to crowd in where they could.1
Houses were being built outside the City for the more prosperous of those driven out. These went to Kensington, Camberwell; to fine wide roads like Sutherland Avenue and to St John's Wood. Many of the poorer had to crowd into the old streets of Lisson Grove. Christchurch, in Bell Street/Cosway Street, that once fashionable church, found itself surrounded by streets and courts of dilapidated, overcrowded houses, split into single-room tenements.
The area between Gray’s Inn Road and St Paul’s was broken into a series of hills and dales by the Fleet River and its various tributaries. This may have been an advantage when the Romans were looking for a strong defensive point, protected by natural barriers but it was a real problem in a busy, commercial city. The streams had long been culverted. They were out of sight so people could forget them. Houses had been built in the valleys but the road still had to go down into one river valley and up to the next ridge time and again, like a switchback. It was very slow, and a great strain on the horses. The traffic became so slow that High Holborn Viaduct and Rosebery Road were built to sail over the existing houses and give quick travel. Today one can look down from various points in both roads and see that the old tenements, which tower above, actually start from several storeys below the bridge level.
The disruption caused by the building of new railway stations, sewers, high roads like Holborn which sails over the old Fleet River Valley, can be imagined. No wonder people fled.