pier, in engineering, term applied to a mass of reinforced concrete or masonry supporting a large structure, such as a bridge. When piers are built on ground of poor bearing value, it is often necessary to drive piles to obtain a firm base. Construction of piers built in riverbeds is facilitated by the use of cofferdams or caissons. Structures that extend out from the shore and over the water, serving as a place to land passengers and merchandise from vessels, are also known as piers. They are used in many harbors when there is ample width of stream; in New York harbor, for example, great economy of shore front is realized by building piers out at right angles to the shore. These piers are generally built on pile foundations. In architecture the term applies to the clustered Gothic pillar, to a wall between openings, and to a detached masonry mass serving as a gate post.