Arx (Roman)

Arx is a Latin word meaning "citadel". In the ancient city of Rome, the arx was located on the northern spur of the Capitoline Hill, and is sometimes specified as the Arx Capitolina.

Rome in 753 BC
The location of the Arx is indicated on this speculative map of Rome circa 753 BC.


At Rome, sentries were traditionally posted on the Arx to watch for signals displayed on the Janiculum if an enemy approached.[1] A red flag would be raised[2] and a trumpet blown.[3] The Arx was not regularly garrisoned, however, and should not be regarded as a "fort." However, in the Gallic siege of Rome (387 BC), the Arx was considered the point of last retreat, the capture of which was synonymous with the capture of the city. It thus held a symbolic power beyond its importance in military strategy, and was a central place in archaic Roman religion.

During the regal period, some members of the elite were permitted to live on the Arx, among them the legendary Sabine leader Titus Tatius. After 384 BC, the Senate banned all private dwellings from the Capitoline Hill, including the Arx. The house of Marcus Manlius Capitolinus, a patrician champion of the plebs who was convicted of seeking kingship, was torn down at this time and later became the site of the Temple of Juno Moneta.

On the Arx was located the auguraculum, the open space where the augurs conducted the rituals that determined whether the gods approved of whatever undertaking was at hand, public business or military action. This auguraculum was the stone where the elected monarch, during the Roman Kingdom, was seated by the augurs with his face to the south.[4]

Major temples on the Arx include that of Juno Moneta (established 344 BC), where the mint was located; Concordia (217 BC); Honor and Virtue;[5] and Vediovis. Jupiter, however, was the god of the Arx.[6]

Other arces

The Romans also referred to the citadel of other cities as an arx (plural arces). Excavations in Cosa, Tuscany, conducted in 1948–54 and 1965–72, uncovered the settlement's arx. Frank E. Brown and his team studied the site extensively when they began the Cosa excavations in 1948. The citadel was a fortified hill on which were built several temples, including the so-called "capitolium" of Cosa.

In Lavinium, south of Rome, Castello Borghese is thought to be the possible site of the Roman-era arx constructed in the port city.

The arx of Londinium was located in the northwest corner of the present-day City of London, south of Cripplegate. It was constructed around 120 and dismantled around the time of Diocletian.


  1. ^ Cassius Dio 37.28.
  2. ^ Livy 4.18.6 and 39.15.11; Festus 103; Macrobius 1.16.15; Servius, note to Aeneid 8.1.
  3. ^ Varro 6.92.
  4. ^ William Ramsay, "An Elementary Manual of Roman Antiquities", (Griffin, 1859, from Harvard University), p. 64.
  5. ^ This was the Aedes Honoris et Virtutis built by Gaius Marius, to be distinguished from the Temple of Honor and Virtue near the Porta Capena.
  6. ^ Jerzy Linderski, "The Augural Law", Aufstieg und Niedergang der römischen Welt II.16 (1986), p. 2226, note 312, and 2291.

Arx, ARX, or ArX may refer to:

Asia-Pacific Research Exchange, a research hub in finance and investment management

ARX (operating system), an operating system

Arx, the aristaless related homeobox gene and protein

Arx, Landes, a commune of the Landes département in France

ArX (revision control), revision control software

ObjectARX, a software API for AutoCAD

Arx (Roman), a Roman citadel, and in particular:

The northern hump of the two forming the Capitoline Hill of ancient Rome

Arx Fatalis, a first person role-playing game developed by Arkane Studios in 2002

Arx, one of Lars Vilks sculptures

Add-Rotate-XOR, see block cipher

Beretta ARX160, an assault rifle

ARX (Algorithmic Research Ltd.), a digital security company

Josef Adolph von Arx (1922-1988), a mycologist who used the botanical author abbreviation Arx


A citadel is the core fortified area of a town or city. It may be a castle, fortress, or fortified center. The term is a diminutive of "city" and thus means "little city", so called because it is a smaller part of the city of which it is the defensive core. Ancient Sparta had a citadel as did many other Greek cities and towns.

In a fortification with bastions, the citadel is the strongest part of the system, sometimes well inside the outer walls and bastions, but often forming part of the outer wall for the sake of economy. It is positioned to be the last line of defense, should the enemy breach the other components of the fortification system. A citadel is also a term of the third part of a medieval castle, with higher walls than the rest. It was to be the last line of defense before the keep.

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