Question: When Virgil wrote "quos ego", what branch of the Indo-European languages was he using?
Sentence (from "Pre-Indo-European languages"): The oldest Indo-European language texts date from 19th century BCE in Kültepe in modern-day Turkey, and while estimates vary widely, spoken Indo-European languages are believed to have developed at the latest by the third millennium BCE (see Proto-Indo-European Urheimat hypotheses).
Relevant evidence: No