Pre Colonial Water System

An ancient Indigenous hand excavated well, approximately 20 to 30 feet deep and roughly two feet in diameter, is fully lined with precisely cut, uniformly shaped stone blocks. The interlocking masonry technique used to fit each stone securely against the next has preserved the structural integrity of the well over many years. Given that the shaft measures only about two feet in diameter narrow enough that a person could scarcely lift their arms overhead how might the builders have positioned and fitted the stone lining within such a confined space?