Mona Passage (mō´nä, –nə), strait, c.80 mi (130 km) wide, between Puerto Rico and the Dominican Republic. Connecting the N Atlantic Ocean with the Caribbean Sea, it is a favored shipping lane, but its waters are treacherous for small craft. At the southern end, midway in the strait, is Mona Island, c.20 sq mi (50 sq km), part of Puerto Rico. It was visited by Columbus in 1493, and in 1508 Ponce de León stopped there. In 1511 the island was ceded to Columbus's younger brother Bartolomé, but it soon became a haven for pirates. Uninhabited, it is a nature reserve, with cliff walls as high as 200 ft (60 m) and caves. A lighthouse is on the north side.