What is the name of the mare where Apollo 11 landed?

The mare where Apollo 11 landed was Mare Tranquillitatis, better known in English as the Sea of Tranquility.

On July 20, 1969, the Apollo 11 Lunar Module Eagle touched down in this broad, dark basalt plain. Neil Armstrong and Buzz Aldrin named their landing site Tranquility Base, while Michael Collins remained in lunar orbit in the command module Columbia. Armstrong’s radio call, “Houston, Tranquility Base here. The Eagle has landed,” made the location famous worldwide.

Mare Tranquillitatis is not an ocean of liquid water. Like other lunar maria, it is a plain formed largely by ancient volcanic basalt that flooded lower terrain and later cooled. The name was assigned in the 17th century by astronomers Francesco Grimaldi and Giovanni Battista Riccioli.

A common mix-up is confusing Mare Tranquillitatis with Mare Serenitatis, another nearby lunar plain. Apollo 11 landed in Tranquillitatis; later missions visited other maria, including Apollo 12 in Oceanus Procellarum.