Sarmizegetusa Regia (also Sarmisegetusa, Sarmisegethusa, Sarmisegethuza, Ζαρμιζεγεθούσα (Zarmizegethousa), Ζερμιζεγεθούση (Zermizegethouse)) was the capital and the most important military, religious and political center of the Dacians. Erected on top of a 1,200 meter high mountain, the fortress was the core of the strategic defensive system in the Orăştie Mountains (in present-day Romania), comprising six citadels. Sarmizegetusa Regia was the capital of Dacia prior to the wars with the Roman Empire.

It should not be confused with Ulpia Traiana Sarmizegetusa, the Roman capital of Dacia built by Roman Emperor Trajan, which was not the Dacian capital, located some 40 km away. Sarmizegetusa Ulpia was discovered earlier, was known already in the early 1900s, and initially confused with the Dacian capital. This inevitably led to inaccuracies regarding Dacian wars and Dacians military system based solely on insufficient information.

Several hypotheses have been advanced to explain the origin of the name Sarmizegetusa. The most important are the following:

Coordinates: 41°53′31″N 12°29′12″E / 41.891967°N 12.486595°E / 41.891967; 12.486595

The Regia was a structure in Ancient Rome in the Roman Forum that originally served as the residence or one of the main headquarters of kings of Rome and later as the office of the Pontifex Maximus, the high priest of Roman religion. It occupied a triangular patch of terrain between the Temple of Vesta, the Temple of Divus Julius and Temple of Antoninus and Faustina. Only the foundations of Republican/Imperial Regia remain. Like the Curia it was destroyed and rebuilt several times, as far back as the Roman monarchy. Studies have found multiple layers of similar buildings with more regular features, prompting the theory that this "Republican Regia" was to have a different use.^{[further explanation needed]}

According to ancient tradition it was built by the second king of Rome, Numa Pompilius as a royal palace. Indeed, the Latin term regia can be translated as royal residence. It is said that he also built the Temple of Vesta and the House of the Vestal Virgins as well as the Domus Publica. This created a central area for political and religious life in the city and Kingdom. When Caesar became Pontifex Maximus he exercised his duties from the Regia.