There is evidence that Antoniadi Crater once contained rivers and lakes. Inverted channels formed from accumulated sediments that were cemented by minerals. These channels eroded into the surface, then the whole area was covered over with sediments. (wikipedia entry)
A crater is a circular depression likely created by an impact event. On Mars large craters are named after deceased scientists, writers and others who have contributed to the lore of Mars. Small creaters (less than 60km) are named after small towns and villages.