And then things really get invested in, in terms of collecting knowledge, as we get into the rule of Al-Rashid's son, Al-Mamun, where he creates in Baghdad what is called the House of Wisdom, which is this center of learning of mathematics, astronomy, physics, medicine, geography, and map-making, poetry, philosophy. And over the next several hundred years, these Abbasid caliphs are going to sponsor scholars from India, learned in Sanskrit, and the ancient Sanskrit texts, and Greek, Chinese, Persian, to translate as much of that knowledge and to collect it in libraries in cities like Baghdad, to translate it into Arabic, and to collect all of that knowledge in one place. And just to get a sense of the type of advances that occurred during this golden age of Islam, which correlates strongly, or is essentially during the Abbasid dynasty, and it ends with the Mongol invasion in the middle of the 13th century, right over here, there are scientists like Al-Khwarizmi. And Al-Khwarizmi is a Persian mathematician and physicist, and he's famous for being the father of algebra. The word algebra that we now have today, and the subject that you can learn a lot about on Khan Academy, it comes from the Arabic word al-jabr, and his book, Al-Kitab Al-Muqtasar Fi Hissab Al-Jabr Wal-Muqabla, which literally means, and those of you who might speak Arabic, or Persian, or even Hindi or Urdu might recognize Kitab is book, and then Hissab is calculation, and al-jabr is an operation of completion, and it's essentially, it's one of the operations we now do in algebra, where you're doing the same thing to both sides of the equation, and balancing, it was also a very similar operation. He also brought the Indian number system, or the Hindu numerals, he brought them to the Islamic empire, and that was really the bridge to bringing it to the West. Famously, Pope Sylvester II, he was educated in Catalonia with the point of acquiring knowledge that was gained from the Arabs.