The “House of Wisdom” continued until 513 when the reactionary wave of orthodoxy had reached even Fatimid Egypt, and in that year it was closed as a home of heresy by the Wazir Afdal. Four years later a new academy near the great palace was founded by the Wazir Maʾmun, but this adhered more strictly to the traditional lines of Muslim study.

In the line of philosophers strictly so-called, that is to say, of those who worked from the basis of Greek science, one is associated with al-Hakim and the Cairo of the Fatimids, namely, Ibn al-Haytsam, known to the mediaeval Latin writers as Alhazen. He was born at Basra in 354, and became distinguished as a student of the Greek philosophers. At that time the path of philosophy was beset with many difficulties owing to the orthodox reaction.

Ibn Sina was a wanderer in many lands, and Ibn al-Haytsam found it more prudent to seek a refuge in Cairo where he made his home amongst the learned of the al-ʾAzhar mosque. He died in 430. We have a long list of the works he produced, all of the type usually associated with the Arabic philosophers, manuals, commentaries, and discussions of questions arising from the teaching of the ancients. In his case these deal chiefly with mathematics, physics, the Aristotelian logic, and the medical works of Galen. The Bodleian contains a MS. of his commentary on Euclid. To the mediaeval west he was best known as the author of a treatise on optics which was translated into Latin and used by Roger Bacon. Occasionally this optical work of “Alhazen” appears in the curricula of the mediaeval universities.

Various evidences of a fanatical spirit in maintaining the doctrines and usages of Shiʿism begin to appear in al-Hakim about 393. In Syria a person was arrested on the charge that he denied that any special devotion was due to ʿAli. The offender was imprisoned by the authority of the Chief Qadi of Egypt who acted as pope over all the territories subject to Fatimid rule, and was examined by four jurists who did their best to persuade him to recognise the Imamate of ʿAli, but, as he remained stubborn, he was beheaded.

In Cairo thirteen persons were arrested for having observed the Salat ad-Duha or “mid-morning prayer,” one of the voluntary observances sometimes added to the five canonical daily prayers, but disapproved by the Shiʿites. The offenders were paraded through the streets, beaten, and detained three days in prison.

In the month of Rabiʿ II. of this same year (393) a man named Aswad Hakami was punished for some offence of which the details are unknown, but which probably was a public championship of the three first Khalifs whom the Shiʿites regarded as usurpers. He was paraded through the city and a herald cried before him: “This is the reward of those who are the partisans of Abu Bakr, and Umar,” after which he was beheaded (As-Suyuti, History, chap. I., Qadir bi-llah).

In 395 al-Hakim re-enforced many old laws against Christians and Jews, and the decrees ordering the strict observance of these penal regulations contained many abusive expressions against Abu Bakr and Umar. A new decree of 395 forbade the use of malukhiya or “Jews’ mallow” as food because it was traditionally stated to have been a favourite article of Muʿawiya the opponent of ʿAli. Similarly the use of jirjir (girgir) or “watercress” was forbidden because it had been introduced by ʿAyesha: and of mutawakkiliya, a herb named after the ʿAbbasid Khalif Mutawakkil. The sale or making of beer (fuqqaʿ) was severely prohibited because it was especially disliked by ʿAli: it was forbidden to use dalinas, a species of small shell fish, for some reason not known: and very strict orders were made against the sale or use of any fish which had no scales.

In the same year a law was published that the noon prayer was to be said at the seventh hour and the afternoon prayer at the ninth, that is to say the modern way of counting the correct hours was to be observed instead of the traditional method of observing the sun. In these cases tradition allowed the noon prayer to be said as soon as the sun is actually seen to begin its decline from the meridian (Bukhari: Sahih ix. 11), and the afternoon prayer after it has declined (id. 13, 13A). Orthodox Islam allows the former at any time between noon and the hour when the shadow of a thing is equal to the thing itself in length, and the latter at any time between the moment of equal shadow and the sunset (cf. id.). The Fatimid Khalif now replaced these very primitive methods of reckoning, which are still in force, by the observance of fixed hours as marked by the dial.

In the month of Safar of 395 al-Hakim caused inscriptions cursing the three first Khalifs, the “usurpers,” and certain others such as Talha, Zubayr, Muʿawiya, and Amru, all regarded as enemies by the Shiʿites, to be written up on the doors of the mosques and of shops, and on the guard houses and in the cemeteries, and compelled the people to display similar inscriptions in gold lettering and bright colours (cf. Maq. ii. 286, As-Suyuti: al-Qaʾim. Ibn Khall. iii. 450). These were extremely offensive to the Sunnis or orthodox who formed the large majority of the people, indeed at the present day the attitude to be observed towards the first three Khalifs is the sorest point of difference between the Sunnis and Shiʿites, and even in recent years more than one Shiʿite has risked death for the sake of spitting on the tomb of ʿUmar. At the same time efforts were made to induce citizens to join the Ismaʿilian sect, and two days were set apart every week for the admission of those who desired to be initiated. On some of these occasions the crowds were so large that several people were crushed to death (Maq. ii. 286).

Those who were keen Shiʿites naturally were encouraged by this legislation to become somewhat aggressive in their attitude. When the caravan of African, that is to say Moroccan and Tunisian, pilgrims on their way home from Mecca passed through Egypt and rested at Cairo, some of the more ardent Shiʿites tried to induce them to utter curses against ʿUmar and the other early Khalifs, and the refusal of the pilgrims to do so led to some disturbances.