What are Billingsgate and Smithfield famously known for in the city of London?

Billingsgate Fish Market is located in Poplar in London which is the United Kingdom's largest inland fish market. It takes its name from Billingsgate, a ward in the south-east corner of the City of London, where the riverside market was originally established. In its original location in the 19th century, Billingsgate was the largest fish market in the world.

Smithfield is a locality in the ward of Farringdon Without situated at the City of London's northwest in central London, England. The principal street of the area is West Smithfield. Smithfield Market, a Grade II listed-covered market building, was designed by Victorian architect Sir Horace Jones in the second half of the 19th century, and is the dominant architectural feature of the area. Some of its original market premises fell into disuse in the late 20th century and faced the prospect of demolition. The Corporation of London's public enquiry in 2012 drew widespread support for an urban regeneration plan intent upon preserving Smithfield's historical identity.

https://en.wikipedia.org/wiki/Smithfield,_London