They couldn’t even tell the time — this uncountable army of believers.

         The warriors of God pushed on to the gates of the imperial city of Constantinople, their arrival heralded by a plague of locusts that destroyed the vines but left the wheat untouched. Their leader, an implacable cleric who had appeared from nowhere to great popular acclaim, exhorted his charges to holy war against the infidel with promises of a home in paradise. Disease and malnutrition were rife. Medical care often involved exorcism of the amputation of injured limbs. Torture and other ordeals settled criminal cases.

         Few had any learning at all. What education there was back home consisted of memorizing outdated texts under the watchful eyes of hidebound doctors of religion. They had no understanding of basic technology, science, or mathematics. They could not date their most important holy days, nor chart the regular movements of the sun, the moon, and the planets. They knew nothing of papermaking or the use of lenses and mirrors, and they had no inkling of the prince of contemporary scientific instruments — the astrolabe. Natural phenomena, such as an eclipse of the moon or a sudden change in weather, terrified them. They though it was black magic.

         The arrival of this fanatical army horrified the locals. Who were these pale-skinned, blue-eyed barbarians, marching under the sign of the cross, and what did they want on Arab shores at the dawn of the twelfth Christian century?

Jonathan Lyons. The House of Wisdom. How the Arabs Transformed

Western Civilization. London: Bloomsbury, 2009. p. 9 (adapted).