There have been 3 incarnations of Exposition Park, the lower field (1882), the upper field (1883), and Exposition Park III (1890). In 1875, the first Allegheny Exposition was held in a hall on the flats along the north shore of the Allegheny River. The Exposition’s goals were to promote Pittsburgh, display local products, and to provide some entertainment. In addition to the hall, there was some open space where horse races, circuses, and concerts were held.
The American Association Alleghenies played baseball games here, in these open fields, starting in 1882.
The Upper Field was hastily created when the lower field (closer to the river) flooded in 1883. Tired of the ballfields on the flood plain, the Alleghenies moved to higher ground at Recreation Park in 1884. The exhibit halls on this Exposition Park site burned down in 1883 and were later rebuilt across the river on the Point.
With the North Side site now largely unoccupied, the new Players League built Exposition Park III very near the site of Three Rivers Stadium in 1890. The Player’s League folded after just one season, and the National League Pirates moved into the park in 1891.
The stadium could seat 10,000 and was quite spatious- 450’ to center and 400’ down the foul lines- typical of the deadball era.
Flooding was always a concern and during a game on July 4, 1902, water covered much of the outfield creating a new rule for the game- anything hit in the water was a ground rule single.
In 1903, Exposition Park was the first National League ballpark to host a World Series game. The Pittsburgh Pirates played games 4,5,6 and 7 of the 8 game series here, and eventually lost to the Boston Americans 5 games to 3.
With the river being so close to the stadium, flooding remained a big issue. Eventually, owner Barney Dreyfuss decided he needed a new ballpark and from there, Forbes Field was born.
See how the Exposition Grounds look on the maps here.