Keystone is also known as capstone, <u>and it is the stone at the highest point of the arch construction.</u> It is placed as the final piece to lock the construction not to fall, as it is distributing the weight of the arch.
<u>B: voussoir</u>
<u>Voussoir is the name of the whole arched part,</u> including keystone and <u>impost</u>. It is the complete curved element, and the blocks included are most usually made out of stone.
<u>C: impost </u>
The impost is the name for the block that lies at the end of the column, a<u>nd it is also used for the block that is the start of the arch-shaped element</u> of the arch. It is the base of the voussoir.
