Mastalos 1 was a primicerius at Rome; he died during the pontificate of Hadrian I (Hadrianos 1), to whom he gave a legacy for distribution to the poor, for the salvation of his soul ("huius denique temporibus defunctus Mastalus primicerius reliquit pro anima sua in potestate praedicti almi pontificis pauperibus Christi de sua propria hereditate erogari"); his heirs then gave or sold properties to Hadrianos 1, including the church of St Leucius five miles from Rome on the Via Flaminia, giving the money raised, 200 solidi, to charity for Mastalos 1's soul; one heir, Gregorios 81, gave his portion of the inheritance to Hadrianos 1 in return for the post of secundicerius: Lib. Pont. 97. 77.

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