This first fascicule of the Final Report on the excavations at Tepe Nush-i Jan, located some 60 km south of Hamadan, provides a detailed account of the five seasons of excavation conducted between 1967 and 1977 as well as a comprehensive description of the temples and associated buildings belonging to the site's main Median occupation. The importance of the site lies principally in the architectural remains constructed in the eighth and seventh centuries BC when the Medes were the dominant population in central western Iran. In the order in which they were built, the monumental buildings of this hill-top sanctuary include an originally isolated tower-like temple which housed a stepped altar on which fire was burnt, a second temple, a strongly fortified storage facility, and a columned hall with three rows of four columns - a forerunner of the famed columned halls of the Persians at Pasargadae and Persepolis. In a remarkable development most of these distinctive structures came to be at least partly filled and encased with stones and mud-brick. As a result, the buildings proved to be in an exceptional state of preservation with intact doorways and, on occasion, intact ceilings as well. Subsequently, probably in the sixth century BC, squatters occupied those structures to which they could still obtain access. Before Tepe Nush-i Jan was investigated there was little or no evidence for the archaeology of the Medes from their own homeland. Today other sites, such as Godin Tepe and Ozbaki Tepe (not to mention fortified 'frontier posts' such as Tell Gubba), can be recognized as belonging to the same culture. Above all else, Nush-i Jan offers a striking picture of the achievements of the Medes, particularly in the field of architecture.