PLYMOUTH SOUND, on the south-west of Devonshire, near the entrance of the English Channel, is one of the famous roadsteads of the world. It is a deep inlet, into which the river Tamar falls from the west, and the river Plym from the east. The extreme seaward boundaries of the bay, from which the Sound, properly so called, opens, are Rame Head (mentioned in Ptolemy) and Stoke Point, not far within which a third river, the Yealm, debouches. The Sound, however, is practically bounded southward by a line drawn from Penlee to Wembury Points, and northward by the Plymouth Hoe. Within these limits its width varies from to 3 miles, while its landward depth is about 3. Immediately within Penlee Point, on the western side, is Cawsand Bay, formerly one of the chief anchorages of the port and navy, but so exposed to the south-easterly gales that it was at times very dangerous; while if vessels anchored in the Sound itself they were open to the full fury of the south-westers. Hence Earl St Vincent pressed forward a scheme for the provision of artificial protection, and in 1812 the construction of the Plymouth Breakwater was begun, from plans prepared by Messrs Rennie and Whidby. This great national work is an insulated mole of stones, a mile in length, stretching across the middle of the Sound, 2 miles from the Hoe, and thoroughly protecting the inner anchorage. It was not completed until 1841, and cost £1,500,000 (see BREAKWATER). About half a mile from the Hoe is a little islet, originally called St Nicholas Island, but now more commonly Drake's Island. This is strongly fortified. A formidable stone fort has also been built on an artificial island immediately within the breakwater; while on either shore there are extensive forts and batteries—at Bovisand and Stamford on the east, and at Picklecombe, Maker, and Tregantle on the west. The estuary of the Plym is called the Cattewater, and is a capacious and important inner mercantile anchorage, opening from the Sound eastward, and protected by the Batten breakwater. The estuary of the Tamar is called the Hamoaze, and from the spot at which it enters the Sound between Devil's Point and Mount Edgcumbe to Saltash is nearly 4 miles in length—a still more valuable and thoroughly protected anchorage for vessels of the largest size, and occupied by men-of-war. In the Channel, 14 miles off the Sound, is the dangerous Eddystone Reef (q.v.), indicated since 1700 by lighthouses, and now rather a directing post to the port than a danger. Plymouth Sound is exceedingly beautiful, and has even been considered worthy of rivalry with the Bay of Naples. On its western shore is Mount Edgcumbe, the delightful seat of the Earl of Mount Edgcumbe, traditionally said to have been selected by Medina Sidonia as his share of the English spoil. Rame Head, crowned by the ruins of a mediæval chapel, is one of the most picturesque headlands on the coast; and the estuary of the Yealm, with the peaked Mewstone at its mouth, is full of romantic beauty.
See R. N. Worth's History of Plymouth (1871; new ed. 1891), and The Three Towns Bibliotheca (1873); L. Jewitt's History of Plymouth (1873); and four works by J. B. Rowe (1873-76).