The object, which dates from the late 12th Century or 13th Century, is in the shape of an animal and would have embellished the ridges of tiled roofs.
It is thought the object was made in the Woolwich area and brought to the city with other pots and roof tiles.
The object was found by the Museum of London during a survey.
Roy Stephenson, head of archaeological collections and archive, said: “This find is relatively rare in the collections of the Museum of London.
“It gives a fascinating insight into the lost roofscape of medieval London, which we know relatively little about.”
He added: “Some of the more common place roofs would have been thatched. But here we have evidence of a decorated tiled roof, possibly from a prestigious private building.”
The finial will now be cleaned and more research on it will be carried out.
Source: BBC News