The land now known as England was originally inhabited by an unknown culture of people, sometimes referred to as "Megalithic" people (a reference to the standing stones they left at, among other places, Stonehenge). These people were displaced by Celtic tribes, who in their turn were pushed back to the peripheries of the island by three Germanic tribes -- the Angles, the Saxons, and the Jutes -- who arrived in the fifth century to fill the power vacuum left by the departing Roman colonizers. We know little of their culture, though, and nothing of their literature, until the moment when they were converted to Christianity -- and literacy -- a couple of centuries later, and some of the earliest texts we know are those used by missionaries to help persuade the Anglo-Saxons of the superiority of Christian belief. In fact, the very oldest written text -- The Dream of the Rood -- survives in part as a runic inscription on a stone cross (shown here). The Dream is a proselytizing poem -- a poem that sought to convert its readers actively. The main speaker of the poem, in fact, is the Cross itself, which explains why it had to allow Christ to be crucified upon it -- a vital "backstory" for the Saxons, who considered crucifixion to be be"fraecodes gealga" -- the thieves' gallows. The cross, in contrast, represents itself as a faithful thegn (military follower) who only did as his Lord commanded, and was rewarded by having a mini-resurrection of his own, uplifted into the light of heaven, where it was covered with gold and rich gems, a hero's reward.
As with modern English, there were several major dialects of Anglo-Saxon: Northumbrian in the North, Kentish in the East, Mercian in the midlands, and West Saxon in the West of England. The political center of the Saxons was in Winchester (Wintanceastre) in the West Saxon area, and thus its speech became the prestige dialect of the language; more than 90% of surviving Old English texts are in this dialect. Much has changed since then, but even to this day, if you look at the top decile of English (the top 10% of our most frequently-used words), nearly all of them are directly descended from closely similar Saxon antecedents: stone (stan); house (hus); was (wæs); say (secgan); father (fæder); and many more.