Smithfield, or West Smithfield, was home to large and famous cattle and sheep markets, indeed, some of the oldest markests in London.
In his Horatian satire of London, "A Description of a City Shower" (1710), Jonathan Swift references Smithfield in an accurate description of London's early 1700s drainage system, in particular as one of the starting points of large amounts of refuse. This makes sense in the context of its meat markets.
Now from all parts the swelling kennels flow,
And bear their trophies with them as they go:
Filth of all hues and odors seem to tell
What street they sailed from, by their sight and smell.
They, as each torrent drives with rapid force,
From Smithfield or St. Pulchre’s shape their course,
And in huge confluence joined at Snow Hill ridge,
Fall from the conduit prone to Holborn Bridge.
Sweepings from butchers’ stalls, dung, guts, and blood,
Drowned puppies, stinking sprats, all drenched in mud,
Dead cats, and turnip tops, come tumbling down the flood. (lines 53-63)