The Isles of Scilly comprise some 55 islands and over 90 rocks lying in the Atlantic Ocean some 28 miles South-West from Lands End on the Cornish mainland. There are five inhabited islands: St Mary's, St Martin's, St Agnes', Tresco , and Bryher, and about 50 others which would be classed as islands. Originally Old Town on St Mary's was the chief centre of population for the Isles, but the centre shifted to Hugh Town in the middle of the 19th century.