The Heritage Gateway's record says that the fort here at The Berth is rather exotic and unusual. It was originally set on two islands in a mere - these days the enclosures are more lumps in a wet meadow, though. They were connected to each other by a causeway of gravel, with another linking them to the surrounding land. Although originally Iron Age, the Berth was used into Roman times and a Roman bronze 'cauldron' was found near the causeway to the land. Berth Pool is on the south side of the mounds - I suppose it must be the remnant of the original mere.
The site first chosen for Baschurch Church was on the top of the Berth Hill. This is a smooth, grassy mound outside the village, crowned by the entrenchments of a British camp, and approached by an ancient causeway leading through marshy meadows beside a deep dark sheet of water called the Berth Pool, of which 'three cart-ropes' will not reach the bottom. But as long as the building was carried on on the Berth Hill, however hard the men worked during the day, 'something,' they knew not what, always pulled their work down again during the night, and threw the stones into the Berth Pool, until at last the disheartened people tried a fresh site, and then their work was allowed to remain.
Elsewhere in the same book (p68):
The same mysterious 'something' which interfered with the building on the height also threw the bells intended for it into the Berth Pool. Horses were brought and fastened to them, but were quite powerless to draw them out. Then oxen were tried with better success; but just as the bells were coming to the surface of the water, one of the men employed in the work let slip an oath, on which they fell back, crying, 'No! never!' And they lie at the bottom of the pool to this day.