It is one of the most important and impressive church in Abruzzo. It was erected on a pagan temple, built in 80 BC, on a hill facing the Adriatic sea, along the so called "Costa dei Trabocchi".
In 1015 the church and the convent were restored by Thrasimund I, Counts of Chieti and the monastery housed Benedictines monks. Around 1060, abbot Oderisius II enlarged and fortified the church with Cistercian decors.
The main façade is characterized by a large marble portal (called Portale della Luna, "Moon portal"), decorated with high-reliefs representing the story of St. John the Baptist.
The church has the typical structure of the Cistercian basilicas, with a nave and two aisles separated by ogival arches and wooden ceiling. In the interior, the apses are beautifully decorated with 13th-century frescos and the stunning cloister is mostly a 20th-century restored structure.