BILLINGSGATE MARKET, the great fish depot of the Metropolis, is now held within the precincts of a picturesque red-brick building, designed by Mr. Bunning, and erected in 1849-53. The name is probably derived from an old settlement of the Saxon Belingas, who formerly possessed this "gate," or "opening," to the River. From the earliest times a market has been held here, and the laws of Athelstan record that at this place a toll was levied upon fishing-boats. William III. made it "a free and open market for all sorts of fish," in 1699.
    The scene presented here, at early morning, is full of life and animation. Fishmongers from all parts of the Metropolis, and from many of the principal inland towns, gather around the salesmen's stalls, which are loaded with salmon from Ireland, Scotland, and Norway; or mackerel from the "narrow seas;" or turbot from the English Channel; and sales are effected, by Dutch auction, in a remarkably simple and expeditious manner. 

Cruchley's London in 1865 : A Handbook for Strangers, 1865