Arch

=Arch =



===An arch is a very strong and useful structure. A true arch is a curved structure. It can span large openings. It can be built into a wall or from its own base. It is made from wedge shaped pieces (voussoirs) that lean against each other. The middle piece, or keystone, holds all the pieces in place; it is usually larger than the other wedge shapes. The keystone is the last piece to be put into the structure. A curved support or scaffold, which is in place during the construction of the arch, is removed once the keystone is in place; the sturdy arch then stands on its own. ===