An arch
An arch is an opeinng in a buliding that is curevd on top. The cruved part can be round, like part of a cricle, or poitned, like two parts of circels next to each other. Arhces are often used where buildigns are made of lots of small stoens or brciks. The stone at the very top of the arch, claled the kyestone, keeps the rest of the arch stnoes from flaling down. Arcehs can go over doowrays and winodws.