the roman wedding introit deus israel (its text extracted from the book of tobit) was assembled during the latter half of the ninth century using two initial and three cadential formulas that pervade the urban repertory of deuterus introits. at least fifteen additional formulas can be identified within this modal group, by far the most numerous among introits at rome. one initial figure stands out from the rest of these formulas, introducing a ‘paschal tone’ incorporating the alleluias regularly interjected into eastertide introits. narrow in range and archaic in style, the paschal tone quotes a roman office antiphon for easter week dating from the seventh century or earlier, whose pitches – the emblematic initial permeating the tone – eventually generated a psalm-tone differentia and a formula used to begin many later deuterus introits, including deus israel.