The Parthian Fortresses of Nisa consist of two tells of Old and New Nisa, indicating the site of one of the earliest and most important cities of the Parthian Empire, a major power from the mid 3rd century BC to the 3rd century AD. They conserve the unexcavated remains of an ancient civilization which skilfully combined its own traditional cultural elements with those of the Hellenistic and Roman west. Archaeological excavations in two parts of the site have revealed richly decorated architecture, illustrative of domestic, state and religious functions. Situated at the crossroads of important commercial and strategic axes, this powerful empire formed a barrier to Roman expansion while serving as an important communication and trading centre between east and west, north and south.

Źródło: World Heritage Convention
http://whc.unesco.org/en/list/1242