The definition of the northern boundary of the state is unusual. Most of the boundary between Delaware and Pennsylvania was originally defined by an arc extending from the cupola of the courthouse in the city of New Castle. This boundary is often referred to as the Twelve-Mile Circle. Although the Twelve-Mile Circle is often claimed to be the only territorial boundary in the U.S. that is a true arc, the Mexican boundary with Texas includes several arcs, and many cities in the South (such as Plains, Georgia) also have circular boundaries.