Samarra is a city in central Iraq, which served as the capital of the Abbasid Caliphate from 836 to 892. Founded by the caliph al-Mu'tasim, Samarra was briefly a major metropolis that stretched dozens of kilometers along the east bank of the Tigris, but was largely abandoned in the latter half of the 9th century, especially following the return of the caliphs to Baghdad. The archeological site of Samarra was named by UNESCO as a World Heritage Site in 2007, calling it "the best-preserved plan of an ancient large city." The modern city bearing the same name lies within the Abbasid ruins.