True History/Ἀληθῆ διηγήματα, by Lucian of Samosata
I wrote this on Sunday, the day of the Greek referendum, when it seemed appropriate to write up a work of classical literature, claimed by some as the first ever science fiction novel. Indeed, it does start rather well, with our hero unwittingly drawn to the Moon where he finds himself embroiled in a space war between the inhabitants of the Moon and the Sun over the colonisation of Venus (strictly Ἑωσφόρος, Lucifer) which seems very close to much more recent tropes of sf narrative. But apart from that particular shaft of forward thinking, it's a fairly standard odyssey tale of going to strange places, seeing strange things and meeting strange people, and I think it is better to let classical scholars hang onto it as a mildly imaginative outlier in classical literature than for sf fans to spuriously (and unnecessarily) claim classical legitimacy for the genre starting here.