The paper deals with the architectural commissions of Atto, during the thirty years in which the religious was first prior general of the Vallombrosani and then bishop of Pistoia (1125-1153). The churches that still have the structure and decorations of the 12th century are particularly analyzed, for example: Santa Maria di Montepiano, San Michele di Plaiano and San Michele di Salvenero in north-western Sardinia, San Paolo a Ripa d'Arno in Pisa and others. Before the year 1140 Atto obtained a relic of san Jacopo the Major, which in 1145 was placed in a chapel in the first two spans of the southern nave of the Cathedral of San Zeno in Pistoia. This chapel was configured as an almost independent space from the rest of the basilica. This initiative brought important artists to Pistoia who exalted the new role of apostolic see of the city and worked in the churches of San Giovanni Fuorcivitas (1162), Sant’Andrea (1166) and San Bartolomeo in Pantano (1167). The incidence of this situation also reverberated on the nearby city of Prato, where the Cathedral (before 1163), despite the autonomist aims of the local clergy, clearly received the constructive influences of the Pistoian Cathedral. The final part of the article analyzes the unfinished church of San Jacopo al Grigliano (1396-1407), in the Province of Verona, which is the most important and majestic sanctuary dedicated to san Jacopo in Northern Italy.