Augustus' propaganda founded the ruler's power on a series of references to the sky: Caesar's comet, which helped to establish the divine nature of kingship, the completion of the calendar's reform celebrated in the Campus Martius' meridian, and Augustus' association with Capricorn, the zodiacal sign of the winter solstice. Various forms of proof derived from texts, works of art and numismatics show the key role of such a ‘power from the stars’. We present here new archaeological and archaeoastronomical evidence coming from Augusta Praetoria Salassorum (modern Aosta), founded around 25 bc after the victory of Augustus' army on the Salassi. An emergency excavation along the Aosta's Roman walls has brought to light, on a corner of one of the towers, an in situ block which carries several reliefs — including a plough and a spade — apparently related to the town's foundation ritual. As a consequence, we carried out a complete analysis of the original urban plan of Aosta and of its relationship with the sky and the landscape, taking into account the complex natural horizon of the Alps in which Aosta's valley is nested. The results show that the town was oriented in such a way as to pinpoint Augustus' ‘cognitive’ relationship with the ‘cosmic’ signs of renewal.