Ancient History
Ancient History is variously defined as lasting until the end of the Roman Empire (476 AD) or as far as the Early Middle Ages. The amount of literature covering this period is understandably vast, but fortunately there is an online depository of books published before 1923, available to all(a). This enormous collection can be downloaded as four large pdf files.
(a) https://archive.org/details/TheRomanHistoryWithNotesHistoricalGeographicalAndCriticalVol1