For the sake of convenience but obviously this has more relevance to Europe than to Islam. The earlier part of the medieval period—the so-called Dark Ages—is not considered to be so dark as was formerly thought to be the case, but little Western cartography survives from this half-millennium. The ultimate expression of the circular world map of the Middle Ages is found in the Ebstorf and the Hereford maps. The most common shape was the circular, disc, or wheel form, a descendant of Greco-Roman cartography, of which two distinct types can be recognized: the T-O and the climatic zonal forms. Both the T-O and the zonal types of circular world maps, which often accompany medieval manuscripts, are also found in the cartography of Islam; in some instances, both concepts are combined on a single map in Christian and in Muslim examples.