This street, jointly with the Langgasse (to the west), are part of the oldest part of the Rechtstadt. Up until the 17th century, both of these streets were referred to as just Langgasse. The name Langer Markt (literally, long market), appeared in the 17th century.
To the east, this market street leads to the the Koggentor (also known as the Green Gate or Brama Zielona today). This gate was built in 1568 and is named Green Gate for the color of its sandstone, and if you stepped through it and crossed Motlau River on the Green Bridge, you'd end up in the Milchkannengasse on the Speicherinsel (Wyspa Spichrzów).
Langer Markt also is the home to some of the most glorious buildings in the city, including the City Hall (Rechtstädtisches Rathaus) and the Artushof (Dwór Artusa). The part of the street between the city hall and the Neptunbrunnen (Neptune's Fountain, Fontanna Neptuna), was named Ferkelmarkt (pigs market) in the 1650s.