At some point in the mid to late fifth century, Patrick wrote a pair of letters, one to a raiding chieftain named Coroticus, and the second to his superiors in the church. Unlike with Gildas, the letters were not designed for public consumption. In fact it is only good fortune on history’s part that these private letters have survived at all.
Their two-dimensional nature makes them simpler to examine than Gildas as well, as they are designed as legal arguments they are not by nature designed to mislead. The letter to Coroticus addresses him as a chieftain and a raider, in fact as the leader who captured several of his congregation. His epistle to the British churchmen makes clear that he has been accused of improprieties in his youth and is designed to explain them away.
As straightforward as they are, they do provide a window into ancient Britain. His letter to a petty chieftain instead of a more powerful king tells us there was no central authority in Britain at the time. That he reported to British churchmen means that Britain was no longer in contact with Rome. The Latin names and titles of his ancestors suggests a continuing sense of Romanitas up to his birth, as does his claim that he was still learning Latin as a part of his education when he was kidnapped by Irish raiders.
Beyond that, we can be certain of next to nothing based on his letters. It is not clear from them when he was active, where he was born, or the political nature of that region.
Medieval legend has it that he alone converted the Irish, but this claim is not to be found in his personal writings. Nor does he say he is an archbishop. These accomplishments were designed to enhance Patrick as a saint but have no foundation in the earliest records.