Pausanias' description of Delphi
The tenth book of the work Description of Greece by the traveler Pausanias (2nd century AD) is dedicated to Phocis; its larger part constitutes a description of the sanctuaries and buildings of Delphi. His work constituted a precious aid to travelers and archaeologists who attempted to identify the monuments revealed by the excavations, although in some cases their identifications were not enough.
Source: Wikipedia — Pausanias' description of Delphi (CC BY-SA 4.0)