Etruria is the region of central Italy north of the Tiber where the Etruscans lived, and what makes its religion distinctive is that the Romans treated it as an applied science rather than as a rival cult. The body of knowledge, which Latin writers called the Etrusca disciplina, covered three main areas: the reading of the entrails and especially the liver of a sacrificed animal, the interpretation of lightning according to which region of the sky it came from and what it struck, and the correct procedure for founding a city, laying out a temple and dividing land.
The underlying assumption was that the sky is divided into regions belonging to particular gods, that the liver of a sacrificial animal maps onto that division, and that a competent reader can therefore work out which god is signalling and about what. A bronze model of a sheep's liver found near Piacenza, marked out in named compartments, is the clearest surviving evidence for the system.
Rome absorbed the discipline rather than suppressing it. Etruscan specialists, the haruspices, were consulted by the Roman state for centuries, particularly after prodigies, and Roman augury and temple orientation carry the same assumptions about a divided sky. The Roman practice of taking auspices before public business belongs to the same family of ideas, and Jerzy Linderski's reconstruction of the augural law shows how technical and how legally binding that procedure had become.