Complex sentence: When he started to dig the foundation, the vessel with the head of John the Baptist was uncovered, but fearful that the relic might be abused by unbelievers, he hid it again in the same place it had been found.
Split into simpler sentences: When he started to dig the foundation, the vessel with the head of John the Baptist was uncovered. But fearful that the relic might be abused by unbelievers, he hid it again in the same place it had been found.