Some steel arch bridges (such as the Navajo Bridge) are built using pure cantilever spans from each side. These are then joined with a pin, usually after forcing the meeting point apart. When the jacks are removed and the bridge decking is added the bridge becomes a truss arch bridge. Such unsupported construction is only possible if suitable rock is available to support the tension in the upper chord of the span during construction, usually limiting this method to the spanning of narrow canyons.