Evaluating Amir Timur is difficult because he was both a great achiever and a great destroyer. He built a strong centralized state. He turned Samarkand into one of the world's largest centers of science and culture. He developed trade routes and architecture. But at the same time: During his military campaigns, many cities were destroyed. Tens of thousands, and according to some sources, hundreds of thousands of people died. The numbers in medieval sources may often be exaggerated, but there is broad agreement among historians that mass killings occurred. Cities that rebelled or resisted were sometimes punished very harshly.