Mare Crisium (the "sea of crises") is a lunar mare located in the Moon's Crisium basin, just northeast of Mare Tranquillitatis. This basin is of the Pre-Imbrian period, 4.55 to 3.85 billion years ago. This mare is 376 miles (605 km) in diameter, and 176,000 km2 in area. It has a very flat floor, with a ring of wrinkled ridge toward its outer boundaries. Ghost craters, craters that have largely been buried under deposits of other material, are located to the south.
The crater has many notable features in and around it. The cape-like feature protruding into the southeast of the mare is Promontorium Agarum. On the western rim of the mare is the palimpsest Yerkes. The crater Picard is located just to the east of Yerkes, and northwest of Picard is the crater Peirce. Mare Anguis can be seen northeast of Mare Crisium. Mare Crisium is the site of the Luna 15 crash in 1969.