Thousands turned out to watch a flock of sheep cross the Millennium Bridge as part of an unusual custom used to mark the start of London Architecture Week.
Architect Richard Rogers helped to launch the sheep drive
About 30 Herdwick sheep left Borough Market for Smithfield Market, making use of the historic droving rights of the Freemen of the City of London.
Architects Richard Rogers and Renzo Piano launched the sheep drive.
Animal rights protesters tried to block the procession's passage onto the bridge but were unsuccessful.
The architects, responsible for Paris' Pompidou Centre, were joined by 10 butchers in full Worshipful Company of Butchers Regalia, sheep dogs, mounted police and several shepherds.
The herd passed in front of St Paul's Cathedral and through Paternoster Square, and were penned in front of St Bartholomew's the Great - one of London's oldest churches - for the St Bartholomew Fair.
They have been supplied by farmer Andrew Sharp who has an organic meat stall at Borough Market, and whose family have been involved in the mutton trade for generations.
Livestock were driven to market in London until the 19th Century.
Peter Ackroyd, historian and author of London: The Biography, said: "It reignites the old human tracks which were used for many centuries by people coming in and out of the city."
The London Architecture Biennale, described as a celebration of architecture and the city, continues for nine days and includes exhibitions, walks, film screenings and debates.