 The first historical mention of the village dates back to 870 AD, when, among the possessions of the abbey of Montecassino, is mentioned a "sancti Petri" on the site of modern Ari.The local monastery, thanks to the economic help given from the Normans, gradually increased reaching the apogee between the 10th and 11th century, when it included a library, an oratory and several possessions such as churches, lands, and mills.Two papal bills, one by Pope Alexander III of 1173 and one by Innocent III of 1208, reaffirm the belonging to the churchood of Chieti, while other privileges are confirmed in a bill of emperor Lothair II.