Abó's first priest, Friar Francisco Fonte, supervised construction of the original San Gregorio de Abó from 1622 to 1627. In 1640, Friar Francisco de Acevedo became guardian there and began renovating the church. When the work was completed in 1651, its massive walls, buttresses, and notched parapets made it resemble one of Mexico's fortress churches. Sandstone walls held together with mud mortar were plastered white with gypsum on the inside and whitewashed adobe on the outside. By 1651, San Gregorio had grown from Fonte's simple, single-naved church into a towering fortress.