Shelter halves are a mainstay of most armies, and are known from the mid 19th century. Often, each soldier carries one shelter-half and half the poles, etc., and they pair off to erect a two-man tent. The size and shape of each half shelter piece may vary from army to army, but are typically rectangular, triangular or lozenge shaped. When time and space allow, some forms of half-shelters can be combined into a larger, more complex tent.