Tyburn, small left-bank tributary of the River Thames, England, its course now wholly within London and below ground. Before it was culverted, the river traversed London from the heights of Hampstead through Regent’s Park to the lower areas of Westminster, where it entered the marshy floodplain of the Thames south of Green Park. One of its branches wandered toward the Thames at the northern end of what is now the Whitehall district, and another entered south of the site of the modern Houses of Parliament. Between was the small gravel island of Westminster. From the 13th century the Tyburn supplied water for London through conduits of elm trunks. Its water is now drained off by sewer. The name Tyburn became famous in connection with the Middlesex Gallows, which stood west of the stream near the modern Marble Arch at the northeastern corner of Hyde Park. It was a place of execution from as early as the 1300s until 1783. Around the gibbet were open galleries for the public.