"shimmering like the mare imbrium"
Map showing location of Mare Imbrium
Creative Commons Attribution Share AlikeMap showing location of Mare Imbrium - Credit: Srbauer

The Mare Imbrium (Latin for ‘Sea of Showers’ or ‘Sea of Rains’) is a vast lunar mare, one of many large, dark, basaltic plains formed by ancient volcanic eruptions on Earth’s Moon.

They were dubbed maria (Latin for 'seas') by early astronomers who mistook them for actual seas.