The official name of the hill was Arx et Capitolium. [1]

A number of stories explain the names of various features of the hill. When workmen were digging for the foundation of the temple of Jupiter on the southern part of the hill, they found a human skull (L. caput, capitalis) of great size. The term Capitolium became synonymous with the temple, its precinct, and eventually the entire hill.

The northern part of the hill was the Arx, the citadel (L. arx) of Rome after the city had expanded sufficiently to include the Quirinal and Viminal hills - the stage of growth commonly known as the City of Four Regions. [1]

The depression between the two summits is known as the Asylum, the place where Romulus is said to have welcomed fugitive slaves from other towns. [2]

The Capitoline was the smallest of the hills of Rome and extended in a general northeast-southwest direction. It was about 460 meters long and had an average width of 180 meters. The northern part of the hill known as the Arx was about 49 meters above sea level and comprised an area of about one hectare. [1]

Historians believe the settlement of the Tiber valley began sometime about 1000 BC, when an outbreak of volcanic eruptions in the Alban hills to the south forced the Latin tribes down into the lowlands. [7]

Ancient tradition maintains that the northern elevation of the Capitoline belonged to the Sabine settlement on the Quirinal. The southern elevation possibly became the possession of the Roman settlement on the Palatine. At any rate, the whole hill became part of the enlarged city known as the City of Four Regions. [8]

During the reign of Servius Tullius, the various elements of the population were amalgamated, and the seven hills, namely, the Palatine, the Capitoline, the Quirinal, the Caelian, the Viminal, the Esquiline, and the Aventine, were covered with houses, and enclosed by a wall about six miles in circuit. [3]

Marcus Furius Camillus erected the temple of Juno Moneta on the Arx in 344 BC. [6]

The Temple of the Capitoline Jupiter was begun by Tarquinius Priscus and completed by Tarquinius Superbus in 535 BC. When the temple burned down in 83 BC, its restoration was started by Sulla and finished by Augustus.

Another fire in AD 80 destroyed some of the finest temples of the city, especially on the Capitoline. Domitian rebuilt the Capitolium with even greater splendor. [2]

The Tabularium, a multi-storied records office built by Q. Lutatius Catulus in 78 BC, rose on the southeast slope of the Capitoline. It was trapezoidal in shape and occupied all the space between the clivus Capitolinus on the southwest and the gradus Monetae on the northeast. [2]

The Capitoline had three distinct parts: a northern elevation (Arx), a southern elevation (Capitolium), and a depression between them (Asylum). [1]

The hill was surrounded by steep cliffs on all sides except the southeast, where it was accessible from the forum valley. The precipitous cliffs at the southwest corner formed the saxum Tarpeium, or Tarpeian Rock, from which criminals convicted of capital offenses were hurled. At the northeast corner was a grassy open space, known as the Auguraculum, where the augurs took their observations. [1]

The principal approach was the clivus Capitolinus, a path from the forum to the depression between the two summits, where it divided. Two flights of steps, the centum gradus and gradus Monetae, led up to the Arx from the forum side. [1]

Titus Tatius lived on the Arx, as well as Marcus Manlius Capitolinus. The house of the latter was destroyed in 384 BC when the senate decreed that henceforth, no patrician should dwell on the Arx or the Capitolium. [1]

Another temple is known to have stood on the Arx, and that was the temple of Concord, dedicated in 217 BC. Two other temples may have been located there: one to Vediovis and one to Honos et Virtus. [1]

There is no record of any other public buildings on the Arx, but private houses extended some distance up the side of the Arx from the low ground below, as they did on the slopes of the Capitolium and to the limits of the Asylum. [1]

A temple to Jupiter Feretrius stood on the Capitolium, associated with an oak tree. [6]

1. Platner, A Topographical Dictionary of Ancient Rome, Capitolinus
2. Lord, The Old Roman World - The Grandeur and Failure of Its Civilization, chapter III
3. The Regionaries Curiosum and Noticia Regio10 - Palatium
5. Connolly and Dodge, The Ancient City, pp. 109-110
6. Platner, A Topographical Dictionary of Ancient Rome, Tabularium
7. Platner, A Topographical Dictionary of Ancient Rome, Arx
8. Platner, A Topographical Dictionary of Ancient Rome, Roma Quadrata