The settlement date of the capital is not known exactly. An inscription discovered at the beginning of the 14th century, in the village Gradiste - Sarmizegetusa says: "On the command of the emperor Cesar Nerva Traianus Augustus, son of the divine Nerva, was settled the Dacian Colony by Decimus Terentius Scaurianus, its governor". The name of the governor shows the the settlement of the new town was done in the first years of the conquering of Dacia (after some opinions in 106-107, after others 108-110).

The settlement of the colony was marked also by the emision of a coin (sestertius) at Rome, from the Senate order, dedicated to "the best ruler", Emperor Trajan.

The choosing of the place of the town by Trajan (Traian) was not at random. The metropolis had some strategic and economic advantages. The Retezat Mountains at the South and Poiana Ruscai Mountains at the North were natural barriers difficult to cross for the eventual invaders. The capital which territorium was from Tibiscum to Micia till the entrance in the Jiu pass, was developing in peace, defended by the Roman camps Tibiscum (today Jupa), Voislova, Micia (Vetel) and Bumbesti.

By Ulpia Traian crossed the imperial road from Danube and made the link between the North of the province to Porolissum (Moigrad).

The antic city had an area of 32 ha surrounded by walls. In the hearth of the city were to main roads (cardo maximus oriented North-South and decumanus maximus oriented East-West), at its crossing being the main public building - Forum. But the city was not only inside the walls. Outside the walls, on a great area, were the villae, the craftsmen workshops (brick makers, glass blowers), the temples and other public or private buildings. Also outside the walls were the cemeteries of the city (sepulcreta) identified at East and also at the West. The population was around 25,000 - 30,000 people.