Medieval Christendom conceived of exactly three revealed religions or laws

Evidence

It was common to speak of there being three revealed religions, three ‘laws’, in the world. Peter the Venerable went to some trouble to prove that only two religions were revealed before the time of Muhammad. The three religions were grouped by the Risalah. Three laws, Judaic, Christian and Islamic, had been given since the beginning of the world, said Humbert of Romans; his fellow-Dominican, Ramén Marti, with more care, said that ‘those who have a law, or who arrogate to themselves the name of a law, are the Jews and the Christians and the Muslims.’ This idea was general, and is reflected by the Emperor Frederick’s famous blasphemy about the three impostors. — Norman Daniel, Islam and the West, 1058

Categorization

• XREF: The ‘three impostors’ theme and the triune scheme of revealed laws echo the framework Daniel sees Muslims reacting to, and could connect to current tripartite religious-mapping debates. — connects to: Some medieval Christians recognized all three faiths worshipped the same one God.