He was also the first Holy Roman emperor, and so it's this region right over here. And they were trading gifts, and this is a historical account. Harun Al-Rashid sends Charlemagne this water clock, and it's so foreign to the Franks, to Charlemagne, that he thinks that it must be some type of magic, that it can't be explained by just normal means. 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.