Complex sentence: One beautiful church which survives is the church of San Francesco jus off the main piazza, the "Piazza Pagano" a treasure of the church is the Byzantine icon of the Madonna del Terremoto.
Split into simpler sentences: One beautiful church that survives is the church of San Francesco just off the main piazza, the "Piazza Pagano". Among the church's treasures is the Byzantine icon of the Madonna del Terremoto.