Celtic Christianity
Despite Rome's later philosophic battles against it, like those at the Synod of Whitby in 664 AD, Celtic Christianity remained the dominant form of Christianity in terms of numbers of adherents for the first thousand years of the Christian era. Most modern Christians do not know this because once Rome either converted, suppressed, or killed the adherents of what they saw as a heresy. They removed all reference to Celtic Christianity's legacy from the libraries of Europe - except the Irish libraries, material being translated only since Irish Independence in the early Twentieth Century.