Portman Estate area remained largely residential, attracting the prosperous middle class who wanted to live near the centre of London. There were also mews for tradesmen and servants. At the southwest corner of the Estate, where Marble Arch now stands, was the Tyburn gallows, London’s principal place of public execution until 1783. Development of the area north of the Marylebone Road around Dorset Square continued after 1815, and to the North West in Lisson Green, workers’ cottages were built from 1820 to 1840. Many of the original Georgian houses north of Portman Square were redeveloped as mansion blocks, which were let on
River Tyburn Avenue in Hampstead. Between St James's Park and Buckingham Palace the waters divided to create two distributaries, creating Thorney Island on which Westminster Abbey was built. Enclosed by concrete, bricks, parks and roads the Tyburn flows through underground conduits for its entire length, including one underneath Buckingham Palace and its course has been used for local sewers which connect to the London sewerage system. Marylebone Lane (W1), which defies the grid pattern of streets, follows the course of the Tyburn on what was its left bank through Marylebone village. From its source at the Shepherd's Well near Fitzjohns Avenue in