The patroness of Arnasco is Our Lady Assumed into Heaven, celebrated on 15 August, with the parish church dedicated to her in the main village, the locality precisely called Chiesa. Reworked in Baroque forms during the 16th century, the building holds fine works of art, including a 17th-century painting of the Baptism of Saint John the Baptist, a statue of the Madonna del Rosario and the marble tabernacle by Gaggini, dated 1536, at the Renaissance high altar.
Arnasco's five hamlets, Villa Chiesa, Menosio, Bezzo, Arveglio and Cenesi, were incorporated in medieval times into the Castellany of Rivernaro, dominion of the Clavesana family: after the earlier Carretto castles of Rivernaro and Costiglione became unusable, in 1321 the castle known as Castel di Bezzo was built, still inhabited today. Only in 1815 did the two largest centres of the former castellany, Bezzo and Menosio, gain their own municipal independence, giving rise to today's municipality of Arnasco.
