Throughout the Roman Empire, Octavian’s Palatine sanctuary of Apollo was one of the most important religious sites in Rome. In absence of evidence, scholars considered the sanctuary a foundation ex novo, dedicated at the site of the Princeps’ own domus in 28 BC. In 2009, my architectural documentation of the sanctuary of Apollo revealed the fragmentary remains of a previously excavated but never identified structure from the Archaic period. It is located directly in front of the Temple of Apollo, the sanctuary’s focal point. Several factors, among them a series of ritual pits, support that it was a sacred building. This discovery fundamentally changes the sanctuary’s architectural and functional pre-history while contributing a new building to the sacred topography of Archaic Rome. In this paper, I discuss the discovery of the site through on-site documentation as well as its architectural reconstruction, ritual functions, and possible historical interpretations.