La Merced Market is a whole neighborhood of markets, many of them simply gigantic. The market began in the old the Barrio Merced. The neighborhood makes up nearly all of the southeast of the Centro Histórico. The market, though, is in the Alcaldía Venustiano Carranza just east of the Centro Histórico.
Many will tell you that the Merced began as a famous monastery. The truth is a little more complicated. With the rise of the colonial city, La Lagunilla, the actual lagoon used to supply the giant and famous market of Tlatelolco (by boat) was no longer navigable. The best docks for supplying the city were here on the east side of the city with direct transport links to the farms in the east and south.
The giant market and all of its satellite markets really began in its present location in 1957. It was a big year for building Mexico City public markets, but just the beginning. During the following administration, that of Adolfo López Mateos (1958 to 1964), no fewer than 88 public markets would be built in Mexico City.