Excerpts from Books and Wikipedia
"Timur the lame (or Tamerlane) captured Baghdad on July 10, 1401, after a siege of six weeks. Despite brave resistance, Timur's attack on the city from seven different directions overwhelmed the defenders. Timur is often considered the last great Mongol conqueror, but though he claimed descent from Genghis Khan and was a nomad by birth, he was probably ethnically and culturally a Turk and a Muslim. He had become emir of Samarkand in 1361 and used it as a base to build a short-lived empire that included much of central Asia, Iran, Iraq, and Afghanistan. After the fall of Baghdad, Timur ordered that every soldier should return with at least two severed human heads, which were then piled high around the city. An estimated 90,000 people died in the massacre, making it one of the worst atrocities of Timur's blood-drenched career. Sparing only the mosques, Timur ordered Baghdad to be burned and the ground leveled. Timur was no simple barbarian, however. He spared the lives of scholars and theologians; many astronomers were sent to Timur's observatory at Samarkand, which became a flourishing cultural center under his rule. However, the city of Baghdad went into a long decline."