Al-Ma'mun spent one day from his treasury one hundred and fifty thousand dinars. This was when he returned from fighting the Romans. He saw that the affairs of Egypt were neglected and he was worried about it, due to what he had heard about the people and the decline of its affairs. He entered it and began to inspect its villages, examining their conditions. It is said that in each village, a platform was set up for him to pitch his tent. He arrived in Fustat on Friday, the 10th of Muharram. The army surrounded him, and he stayed in the palace. He continued to investigate the roots of corruption and eliminate them until he left Egypt at the end of Safar of that year, heading to Damascus. Al-Ma'mun, during his reign, was concerned with organizing its affairs, reforming its internal matters, and strengthening its foundations and its rulers. He ordered the repair of the Nile gauge built by Usama in al-Rawda and the construction of a mosque there, and another gauge in Banbud, and the repair of the gauge of Ahmad. After Al-Ma'mun left Egypt, he was informed that the diwans in Egypt were operating in a manner that did not satisfy him, by accepting increases and canceling guarantee contracts, and taking them from those who had endured hardship and effort in repairing and developing them, and handing them over to those who paid the increase without cost or effort. When he learned of this, he forbade it and issued his strict orders to dismiss all officials, guarantors, and administrators from accepting increases, and to confiscate what they possessed and took possession of as long as they were closed and their installments were paid. This included a decree that was read to the people, reminding them of what is stated in the Holy Book: "O you who have believed, fulfill the contracts." On the 19th of Rajab in the year 218 AH, Caliph Al-Ma'mun died after a severe fever on the river. He was in Tarsus in Cilicia and was buried in Tarsus. His reign lasted 20 years and a few months, and his caliphate lasted 20 years and five months. Al-Ma'mun's legacy is the legacy of the caliphs, as it indicates what he achieved and the extent of industry and perfection. His strong attachment to science and industry led him to practice them himself and to support them. He spared no effort or expense in advancing them. If it were not for him, the Arabs would have lost many works written in Persian, Syriac, Greek, Indian, or Latin. He was the one who sought to translate them into Arabic and encouraged his subjects to read them and benefit from them. His contribution in this regard is not limited to the speakers of the Arabic language, as the people of Europe are generally indebted to him because he preserved for them many Greek and Latin books, without which they would have been lost if they had not been translated into Arabic and preserved for the ages.