Sarmizegetusa Regia (also known as Sarmisegetusa, Sarmisegethusa, Sarmisegethuza; Ancient Greek: Ζαρμιζεγεθούσα, romanized: Zarmizegethoúsa) was the capital and the most important military, religious and political centre of the Dacians before the wars with the Roman Empire. Built on top of a 1200 m high mountain, the fortress, consisting of six citadels, was the core of a strategic and defensive system in the Orăștie Mountains (in present-day Romania). The archaeological site of Sarmizegetusa Regia is located in the village of Grădiștea de Munte in Hunedoara County.

Sarmizegetusa Regia should not be confused with Ulpia Traiana Sarmizegetusa, the Roman capital of Dacia built by Roman Emperor Trajan some 40 km away, which was not the Dacian capital. Sarmizegetusa Ulpia was discovered earlier, was known already in the early 1900s, and was initially mistaken for the Dacian capital, a confusion which led to incorrect conclusions being made regarding the military history and organization of the Dacians.

The pronunciation in the Dacian language is not known for certain, nor is the meaning of the word. Several hypotheses have been advanced to explain the origin of the name Sarmizegetusa. The most important of these ascribe the following possible meanings to the city's name:

Sarmizegetusa Regia contained a citadel, the largest of the Dacian fortifications, and residential areas with dwellings and workshops as well as a sacred zone.

The archaeological inventory found at the site demonstrates that Dacian society had a relatively high standard of living.

The citadel wall was 3 m thick and about 4 – 5 m high at the time of its completion. Because the wall, which encloses an area of about 3 ha, is built to follow the edges of the height, the citadel has a more unusual configuration, that of a hexagon with unequal sides. Nearby, to the west, there is an extensive civil settlement covering an area of 3 km, where many dwellings, workshops, warehouses, barns, and water reservoirs can be observed. 100 meters to the east, right at the citadel gate on the same cardinal point, are the sanctuaries, which have varied shapes and sizes. The sanctuaries were located on a terrace, which had been connected to the aforementioned gate by a paved road. It is not known whether there were seven or eight quadrilateral sanctuaries, as they were destroyed by the Romans during hostilities and it cannot be determined whether it was a single large sanctuary or two smaller ones built very close together. There are only two circular sanctuaries.

Historical records show considerable variation in the spelling of the name of the Dacian capital:

Towards the end of his reign, Burebista transferred the Geto-Dacian capital from Argedava to Sarmizegetusa. Serving as the Dacian capital for at least one and a half centuries, Sarmizegethusa reached its zenith under King Decebal. Archaeological findings suggest that the Dacian god Zalmoxis and his chief priest had an important role in Dacian society at this time. They have also shed new light on the political, economic and scientific development of the Dacians and their successful assimilation of technical and scientific knowledge from the Greek and Romans.