The original boundaries of the District of Columbia were marked using boundary stones. These were made of saw-cut sandstone blocks and stood two feet high when set in the ground. Ten boundary stones were placed along each side of the 100 square mile (259 square kilometer) district of Columbia. Although the original surveyors intended each side to be ten miles (16 kilometers) long, their measurements were often inaccurate, resulting in the sometimes significant misplacement of stones and the overall skewing of the District boundaries. Some of these discrepancies are intentional, because the ground at the exact mile point was covered in water; "in such cases", Andrew Ellicott, the leader of the surveying crew, noted in 1793, "the stones are placed on the nearest firm ground and the true distance in miles and poles is marked on them".