It has long been suspected that much of the Inca road network used or modified existing roads. However, few of the many sophisticated and powerful pre-incan civilizations would have had either the need or the resources to build the long stretches of interregional highway —across often sparsely populated and marginal terrain— needed to first conquer, and then govern, such a far-flung empire. Evidence uncovered by the South Central Andes Ancient Roads Project and reported here suggests that just such an imperial artery was built by the Wari through the upper tributary valleys of the Nasca River and across the high-elevation grasslands of the Pampa Galeras during the Middle Horizon (A.D. 650- 1000). The route would have connected the south coast with the Andean highlands over half a millennium before the initial Inca wars of conquest and the founding of Tawantinsuyu.