The legionary base at Legio (Legion II Trajana and Legion VI Ferrata) is the first full-scale legionary base of the Principate excavated in the Eastern Empire. The 2015–2019 excavation seasons of the Jezreel Valley Regional Project focused on the headquarters compound, the principia. While many components of the compound are typical of those of permanent legionary bases throughout the Empire, several unique features of the principia at Legio offer new research avenues concerning the function of these buildings within the Roman army administrative system and community life. This paper summarizes the results of the 2015–2019 seasons of excavation and remote sensing within the principia.