The patron saint of San Giovanni in Galdo is Saint John the Baptist, celebrated on 29 August. The ancient village grew up precisely around the church dedicated to him, of which some parts of the perimeter walls remain, today incorporated into the new structure of the town hall; only between the 9th and 10th centuries, with the settlement of the territory's higher areas, did the village begin to take shape around the ancient church and the castle, so much so that by the 11th century there is already record of San Giovanni in Galdo as a castrum, a fortified settlement.
In the old village, besides the church of San Giovanni Battista, the old abbatial palace, Palazzo Ruffo, is still visible, along with the fine-grained urban fabric typical of many Molise historic centres. The earliest traces of settlement in the municipal territory, however, date back to the 2nd century BC, when a small Italic Samnite temple was built on Colle Rimontato, near the present-day settlement, whose remains can still be identified today.
