Another beach obstacle was the log ramp. This was nine to ten feet high, consisting of two upright logs driven into the sand, one short and one long, with a third log placed on top slanting backwards from the sea. This was constructed to catch an incoming landing craft and slide it upward towards the mine placed on the end. Stakes pointing seaward with mines attached were a variation of this, but perhaps the most commonly used obstacle was the hedgehog or tetrahedron or "element C" as it was variously called. This was an ingenious contrivance of three steel rails, riveted together and flattened on their ends to prevent sinking too far into the sand. All these devices were used in combination, usually with "Belgian Gates" and log ramps, forming an outer barrier with hedgehogs and stakes thickly placed inside all along the beach. Some of the beaches were found to be much more formidable in barriers than others.