Dome (Latin domus, a house). In the early Middle Ages the word domus was applied to the house of God, and especially to the cathedral church. In this latter sense the derivatives of the word are still used in Italy and Germany. The word dome is used more generally in architecture to signify the roof to the whole or a part of a building, which roof has a circular or polygonal base, and whose perpendicular section is a curved line. Such domes, or curved roofs, are found very early in the history of architecture, especially in Etruria and Persia. The dome of modern architecture has its origin in the Roman adaptation of the Etruscan dome. The roof of the Pantheon at Rome is the finest example existing of the ancient Roman dome. In the Byzantine architecture, a flat dome over the center of church edifices, resting upon four arches, and supported below by half or quarter domes, is copied in the Turkish religious architecture. A modification of the Byzantine into the horse-shoe dome has been introduced largely into the Russian and some other Oriental branches of architecture. In the transition from the Byzantine to the Romanesque style of architecture, the dome became more of a cupola. In the Gothic architecture the dome disappeared. The Baptistery at Pisa, founded in the 13th century, has a dome for a roof, though all the ornaments are Gothic. It was during the Renaissance, that the modern dome was developed. The first one built was in the church of Santo Spirito, in Florence. It had a semicircle for its section, and was single. The dome of the cathedral of Florence has a diameter of 139 feet, the same as that of St. Peter's in Rome, and only three feet less than that of the Pantheon at Rome. This dome is considered by some to be more elegant in outline than that of St. Peter's, which others consider the most graceful dome ever built. Both rest on a cylinder, or drum, and both are double; that is, they have each an interior dome, surmounted by an exterior one, rising from the same base, and being more pointed. This exterior one is only for its effect on the external architecture. They are both surmounted by a small cupola, called a lantern. All later Renaissance domes are built on this general type. Among the most famous domes are the following: Pantheon, Rome, 143 feet in diameter; Cathedral, Florence, 139; St. Peter's, Rome, 139; St. Sophia, Constantinople, 115; St. Paul's, London, 112; Mosque of Achmet, Constantinople, 92; Church of the Invalids, Paris, 80; St. Vitalis, Ravenna, 55; St. Mark's, Venice, 44. — Maigne, Dictionnaire des origines dans les arts (Paris, 1864); Lubke, Geschichte der Baukunst; Viollet le Due, Dictionnaire de l'Architecture (Paris).