Plymouth Sound is a deep inlet, 2 1/2 to 3 miles wide, and 3 deep, into which the river Tamar falls from the west, and the river Plym from the east. It is sheltered by a great breakwater, constructed in 1812-41 at a cost of £1,300,000 - an insulated mole of stones, a mile in length, stretching across the middle of the Sound, 2 miles from the Hoe. About half a mile from the Hoe is a little islet, Drake's Island, which 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. The estuary of the Plym is called the Cattewater, and is a capacious inner mercantile anchorage, 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 thoroughly protected anchorage for vessels of the largest size, and occupied by men-of-war. Plymouth Sound is exceedingly beautiful, and has even been likened to the Bay of Naples. On its western shore is Mount Edgcumbe, the delightful seat of the Earl of Mount Edgcumbe. Picturesque Rame Head is crowned by the ruins of a mediaeval chapel; and the Yealm's estuary, with the peaked Mewstone at its mouth, is full of romantic beauty.

See Worth's History of Plymouth (1871; new ed. 1891), and The Three Towns Bibliotheca (1873); Jewitt's History of Plymouth (1873); and four works by J. B. Rowe (1873-76).