A pair of key stones placed on both sides of the entrance to a stone bridge. In addition to their practical utility in securing the stone or stones forming the bridge itself, they are also an important design element expressing the bridge's sense of stability. They are used not only with stone bridges but also with wooden and earthen bridges. Ordinarily they are placed at both ends totaling four stones, but sometimes a portion of these will be omitted.
Japanese Garden Dictionary: A Glossary for Japanese Gardens and Their History
(C) 2010 by Ono Kenkichi and Walter Edwards. All rights reserved.