Capitol (Lat. Capitolium), the great national temple of ancient Rome, situated on the southern summit of the Mons Capitolinus, the smallest but most famous of the seven hills on which Rome was built. The hill is an irregular oblong in figure, about three-quarters of a mile in circumference at its base, running from north-east to south-west, and terminating at its southern extremity within 250 yards of the river in a precipice with an abrupt fall of 80 feet—the 'Tarpeian Rock,' over which state-criminals were thrown. On its northern summit, the higher and steeper of the two, stood the Arx or citadel of Rome, the site of which is now occupied by the church of S. Maria in Araceli. Since the whole hill was fortified and regarded as the natural defence of the city, Arx is not unfrequently used as if synonymous with Mons Capitolinus, and similarly from the importance and reverence attaching to the temple the name Capitolium often means the whole hill. The Capitol was founded by Tarquinius Priscus, and completed by Tarquinius Superbus. It was burned down during the civil wars (83 B.C.), was rebuilt by Sulla, was burned again by the soldiers of Vitellius (69 A.D.), rebuilt by Vespasian, but burned a third time in the reign of Titus (80), and splendidly restored by Domitian, whose structure lasted to a late period of the empire. The original ground-plan, however, with that rigid conservatism so characteristic of Roman law and religion, was never altered. The temple comprised three distinct cells (cellæ), enclosed by one roof, the middle cell dedicated to Jupiter, those on either side to Juno and Minerva. In the Capitol the Sibylline books were stored, and here the consuls on entering upon office offered up sacrifices and made their vows; hither also the victorious general on his triumph was borne in his triumphal car to give thanks to Jupiter.
The modern Capitol (Campidoglio), built on the site, and part of the basement of the ancient Capitol, was designed by Michael Angelo, but is one of his inferior works. It is used as a kind of hôtel-de-ville and museum.
On the Capitoline Mount there was also the temple of Jupiter Tonans, built by the Emperor Augustus; and the magnificent Tabularium (built by Quintus Catulus, 73 B.C.), containing archives. For the U. S. Capitol, see WASHINGTON; the state capitols are mentioned in the articles on the state capitals, ALBANY, AUSTIN, &c.