Poltava by Aleksandr Pushkin (1829) — An epic poem about the Battle of Poltava and the figures caught up in it: Peter the Great, Charles XII, Hetman Mazepa, and the young Ukrainian woman Mazepa loved. Pushkin's portrait of Mazepa is hostile (he is cast as a traitor and villain), which made the poem politically controversial in Ukraine from the start. Read it to understand how Russia mythologised the battle — and why that mythology remains contested.
Eneida by Ivan Kotlyarevsky (1798) — The founding text of modern Ukrainian literature, written right here in Poltava. Kotlyarevsky took Virgil's Aeneid and transplanted it wholesale into the world of Ukrainian Cossacks: Aeneas becomes a Cossack chief, his crew a band of rowdy Zaporozhian soldiers. The result is ribald, funny, and full of precise detail about Cossack life, customs, and language. It reads like nothing else from its era.
Evenings on a Farm Near Dikanka by Nikolai Gogol (1831–32) — Gogol grew up in the Poltava region and set these early stories in the Ukrainian countryside he knew as a child. They are comic, supernatural, and rich in Ukrainian folk culture: witches, devils, Cossack ghosts, and village life. Poltava and the surrounding villages feel recognisable in them even now.
The Cossack Hetmanate by Serhii Plokhy (various works) — Plokhy, the pre-eminent Western historian of Ukraine, has written extensively on the Cossack period and on the Battle of Poltava's aftermath. His The Origins of the Slavic Nations and The Gates of Europe both address what the battle meant for Ukraine's subsequent absorption into the Russian Empire. Essential background for understanding what you are looking at when you stand at the battlefield.