This thesis examines the changing form and function of non-funerary cult buildings in early Latial and Etruscan settlements in order to better describe and understand the advent of monumental temples in the archaeological record. It draws on a significant quantity of material excavated in the past forty years and developments in relevant theoretical frameworks to reconstruct the changing appearance of cult buildings from huts to shrines and temples (Chapters 2 to 4), and to place monumental examples within wider religious, topographical, and functional contexts (Chapters 5 to 7). This broader perspective allows a more accurate assessment of the extent to which monumental temples represent continuity and discontinuity with earlier religious architecture, and furthermore clarifies the respective roles of Latium and Etruria in the transformation of cult buildings into distinctive, prominent parts of the built environment. Although it is possible to find many different accounts of religious monumentalisation in existing scholarship, this thesis holds that traditional narratives no longer accurately reflect the archaeological evidence. It sets out a sequence of developments in which early religious architecture was a dynamic, rather than conservative, phenomenon. It demonstrates that temples were not the inevitable product of a natural progression from open-air votive deposition to monumentality, or simply an imported concept, but rather a deliberate response to the opportunities offered by an increasingly mobile Mediterranean population. It also contends that Latium played a more important role in formulating the characteristic components and functions of central Italic temples than previously thought. This thesis consequently offers a new account of early religious architecture in western central Italy as well as an alternative interpretation of its monumentalisation.