Britain in the wider sense is the frame for material that crosses the island's internal borders. Roman Britain left altars and temples to a mixture of imported and local gods, and the fusions recorded on them, Sulis Minerva at the hot spring at Bath above all, are among the clearest evidence anywhere for how Roman religion absorbed a provincial cult rather than replacing it. What came after the legions is much thinner. The Anglo-Saxon settlement brought a Germanic pantheon known mostly from place names, the days of the week and a handful of hostile Christian references, and the Norse settlement of the north and the isles brought a related one.
Both peoples brought runes, and the inscriptions they cut are the earliest writing in the island's vernaculars. English runic inscriptions run from small personal objects to the standing cross at Ruthwell, and reading them is a discipline of its own, because the alphabet was extended for English sounds and most of the texts are very short.
The Reformation crossed the internal borders and produced a different result on each side of them, which is why the atlas keeps England, Scotland and Ireland as separate entries and uses this one for what genuinely spans them: the print culture that carried reformed argument in a shared language, the Bible translations that circulated across the whole island, and the dissenting movements, Quakers, Baptists and Methodists among them, that organised without regard to the border and then exported themselves.