This chapter sets out a new proposal for a coherent interdisciplinary prehistory of the Andes, based firstly on a long overdue reexamination of the relationships between the various regional ‘dialects’ within the Quechua language family; and secondly on the search for a far more satisfactory correlation with the archaeological record.Our founding principle is that language expansions do not ‘just happen’. Rather, they happen only for those very same reasons of socio-cultural change that archaeology seeks to describe through its own, independent data. Here is the true link between our disciplines, so we discard outdated, facile equations of ‘language equals culture equals genes’, in favour of the real correlation: that language families necessarily reflect past expansive processes, whose traces should also be clear in the material culture record. This principle is one that we can make use of to identify and assess correspondences between archaeological and linguistic patterns, on three levels: chronology, geography, and above all, causation. Or in other words: when, where and why did particular language expansions occur?In the Andes, in principle this entails that we should look to the Horizons, not the Intermediate Periods, as offering the most natural explanations for the major Quechua and Aymara dispersals. With the Incas too late to account for the time-depth of either family, the most plausible candidate for the first major expansion of Quechua turns out in our view to be the Wari Middle Horizon, with the Chavín Early Horizon more tentatively suggested as behind the earlier spread of the Aymara family. This effectively both upturns the traditional Torero hypothesis, and bears clear implications for the long debate in archaeology as to the nature, duration and extent of ‘Horizons’.