Homer, one of the greatest poets of Ancient Greece was considered to have written wrote two poems about Ancient Troy, The Illiad, and The Odyssey.
Modern scholars disagree on whether Homer wrote it by himself or whether a group of authors did the work in his name. All parties agree that the poem was modified over the years, written language was not invented in those days.
Ancient Greek poems were not written down, but they were sung by bards, people specially trained to memorize these poems and pass them down orally. The bards considered that the poems they recited were actual history, but most of the time, they were just tall tales of actual events that happened.
Homer wrote the story of the Trojan war as he heard it from a bard who was reciting it.