The freestanding arch has long been used as a symbol for countries around the world and you will find that these arches often fall into two categories: gateway or triumphal.
A freestanding "gateway arch" is a symbol of the passing from one realm into the next, both in a physical and spiritual sense. The Japanese Torii (shown below) would be a symbol of passing from everyday life into a sacred space.
The triumphal arch dates from Roman times. This arch is a symbol celebrating victory in war, or the leader of such a victory. Its form is also often used as a memorial to fallen soldiers of a war such as the U.S. Civil War Memorial from Hartford, Connecticut shown below.
Your charge is to find and waymark the freestanding arches of the world, gateway or triumphal, ancient or modern. No backyard or garden trellis arches will be accepted. Arches over highways and roadways will be considered on a case by case basis.