The term semiregular is used to describe polyhedra that are uniform but not regular. The semiregular convex polyhedra include thirteen solids associated with another ancient mathematician, Archimedes. He lived after Euclid and worked in Syracuse on the Mediterranean island of Sicily. These objects are called Archimedean solids. There also are an infinite number of semiregular prisms. These have like regular polygons on the top and bottom and straight lines joining the vertices of these to form the square sides. A second infinite group of semiregular solids are called antiprisms. These also have like polygons for top and bottom, but twisted so that each vertex of one polygon is joined to two vertices of the other to form an equilateral triangle.