Callao, a fortified town of Peru, the principal seaport of the republic, on the river Rimac, in the department and 6 m. W. of Lima, of which city it is the port; lat. 12° 6' S., Ion. 77° 14' W.; pop. in 1871 estimated at 27,000, of whom 17,000 were natives, 5,000 Italians, 300 Germans, 2,000 British subjects, 500 French, 700 North Americans, and 1,500 Chilians and Ecuadorians. The harbor is defended by three forts with an armament of 200 guns, and is sheltered toward the south by the barren island of San Lorenzo, 9 m. in circumference, and whose highest point is 600 feet above the level of the sea. The present town is three quarters of a mile from the original site. The houses were formerly for the most part low and of miserable appearance, having until lately been rarely constructed of other materials than mud, with flat roofs and only one story, owing to the frequency of earthquakes. There is, however, parallel to the bay, a handsome street with a number of good edifices and private dwellings of two stories. The roofs are often of hardened mud, as it never rains here, the only moisture proceeding from an occasional thick drizzling mist. Ship loads of wheat are at times seen piled up on the mole for weeks together without any shelter.

The heat at Callao is very great, and natives and foreigners suffer from severe attacks of ague. Miasmatic affections are also very common, the miasma probably proceeding from the outskirts of the town, which are covered with a coarse grass, with here and there a few very small pools of stagnant water. The atmosphere is sometimes loaded with foul smells, especially that peculiar one which may be perceived in almost every town within the tropics. The old castle or fortress has been dismantled and converted into a custom house. The market is situated in a square occupying an acre and a half. The commerce at this port has been steadily growing in importance since its foundation. The chief exports are guano, nitrate of soda, borate of lime, opium, cochineal, and Peruvian bark. The total value of the exports during the year ending Sept. 30,1871, was $12,959,289 41; and that of the imports, $15,669,655. In the same year the port movements were as follows: Entered, 7 steamers, of 6,932 tons, and 460 sailing vessels, of 370,806 tons; cleared, 7 steamers, of 6,942 tons, and 455 sailing vessels, of 366,-601 tons.

The town has railway and telegraph communication with Lima. - Callao was besieged for five months in 1624 by the British pirate Clark, who died there without having been able to take it. It was incorporated as a town in 1671. It was completely submerged with all its inhabitants during the memorable earthquake of 1746, and the ruins are still distinguishable under water when the sea is calm. In 1820 its harbor was the scene of a naval combat between the independents of Chili and the Spaniards, who were defeated, and in September of the following year surrendered Callao, their last foothold in Peru. In 1825 it was almost entirely submerged by a volcanic upheaval of the ocean, and again in August, 1868.