Anfiteatro Castrense

it.wikipedia dates it to 218-222 AD and says that «con tutta probabilità fu costruito dall'imperatore Eliogabalo … come anfiteatro di corte annesso alla dimora imperiale sessoriana». It stayed in use until the Aurelian Walls cut it in half and turned it into a forward bastion by blocking the arches of its façade. The Sovrintendenza Capitolina records that the elevation was originally three orders of arcades, entirely in brick, and was reduced to the first order for defensive reasons under Paul IV in the sixteenth century, and that the concrete foundations are exposed today because the surrounding ground level dropped.