It's really interesting reading Al-Khwarizmi writing back and forth with Ibn Sina speculating about life on other planets and whether they might have been visit

It's really interesting reading Al-Khwarizmi writing back and forth with Ibn Sina speculating about life on other planets and whether they might have been visited by prophets too. Much, though not all, of the big scientific work in the Islamic world was in Iran and central Asia. But eventually enlightenment led to counter enlightenment and the rise of Gnosticism and mysticism. Then the Mongols rode in and killed everyone. They were normally good about capturing cities in an economically useful state, especially if they surrendered, but Ala ad-Din Muhammad II really pissed of Genghis Khan who was mostly busy with China at the time and couldn't spare the troops for a conquest, just an invasion. So they killed everyone in the cities except a few hundred they shipped back to Mongolia. Then came back a few weeks later and killed any survivors who had come out of hiding. And central Asia went from a trade nexus with possibly the largest cities in the world to the state we know it in today.