The lunar maria (pronounced /ˈmɑri.ə/; singular: mare, two syllables /ˈmɑreɪ) are large, dark, basaltic plains on Earth's Moon, formed by ancient volcanic eruptions. They were dubbed maria, Latin for "seas", by early astronomers who mistook them for actual seas. They are less reflective than the "highlands" as a result of their iron-rich compositions, and hence appear dark to the naked eye.