The Mosque-Cathedral of Cordoba (World Heritage Site since 1984) is arguably the most significant monument in the whole of the western Moslem World. The mosque was built in the hypostyle, the earliest style of mosque architecture. The interior of the mosque features the forest of columns that has come to define the hypostyle type.The building itself was expanded over two hundred years. It is built with recycled ancient Roman columns from which sprout a striking combination of two-tiered, symmetrical arches, formed of stone and red brick.