The Medinans welcomed Mohammed as a sagacious leader and arbiter of disputes, and he shrewdly used this reputation to build a power base. This allowed him to eventually unite the entire peninsula of Arabia under his authority and to organize a potent new military force inspired by his new religion of self-sacrifice and devotion to God. By 630 he had conquered his former home town of Mecca, where the people now embraced his religion.
Then Mohammed died on 8 June 632.
His death threw his followers into a state of confusion, but only briefly, as one of Mohammed’s most important disciples, his brother-in-law Abu Bakr, took over as the first khalifat rasul-Allah--‘successor to the apostle of God’--or caliph. This did not settle the leadership crisis then or afterwards. But it did allow the Arabs to take advantage of their newfound unity and their religiously inspired warriors to launch a rampage of conquest that within two decades of the Prophet’s death crushed the armies of Persia, overran Egypt, Syria and parts of Asia Minor, and nearly took Byzantium.
In a second wave of conquests from 696 to the 720s the armies of Islam pushed north to the Caspian Sea and Turkestan, northeast into modern Iran up to the Aral Sea, and even briefly into Kashgar, on the edge of China’s sphere of influence. To the southeast they conquered the lower Indus Valley. In the west they seized North Africa and raged into Spain, turning back only when they reached France and were confronted by a powerful Frankish army led by Charlemagne’s grandfather, Charles Martel.
By the mid-eighth century the expansionist military force of Islam was largely spent for the moment, and the Arabs began to take stock of what they had conquered--politically, economically and culturally. Having come from a desert where few were literate and the lifestyle modest, they brought little material culture to the ancient civilizations now under their sway. Their significant contributions were language and religion, and this is where their talent as master assimilators came into the fore, as they seized on the clothing, dress, architecture, philosophy, literature--and science--of the Persians, Greeks and Indians they now ruled.
The possibilities offered by this crucible of cultural interaction burst forth just over a century after Mohammed’s death when al-Mansur built his magnificent new city as a symbol of his awesome power and of learning. Urbane and sophisticated, al-Mansur and the early Abbasids lavished the wealth and power of their empire on science and the arts. The Arabs’ golden age of literature, architecture and science, centred in Baghdad, reached its apex during the reigns of al-Mansur’s successors Haroun ar-Rashid (ruled 786-809) and his son al-Mamun (ruled 809-833). This was when the Indian texts first brought by Kanaka, and the others that came later, were translated, organized and studied along with the knowledge of the ancients from Greece and Persia, and eventually synthesized into the forms that would later reach Europe.
Sir Richard Burton, the nineteenth-century explorer and orientalist, compared Baghdad during its glory years to the Paris of his century, a city that would also have rivalled Rome at its height. But the truth is that no one will ever know for sure the splendour that was Baghdad, for it was utterly destroyed, almost to the last brick, first during a period of civil war among the later Abbasids, and then in 1258 by an invading Mongol army.
At the core of Baghdad was a massive inner city of palaces, administrative buildings and army barracks. Known as the Round City, it stretched for two miles in diameter, and was ringed by three concentric walls. In the centre stood the caliph’s Golden Palace, on an axis where four highways radiated outwards in cardinal directions to the four corners of the empire. Surrounding the Round City were suburbs that grew up in all directions. These included sections for Jews and Christians, considered adherents of sister religions to Islam, and several large compounds for monasteries built by the Nestorian sect of Christianity. Banished two centuries earlier by Justinian, the Nestorians brought to Baghdad stacks of Greek scientific texts, which they helped translate into Arabic.
Someone walking through the hot, sunny streets of this Mesopotamian city in 800, the same year that Charlemagne was crowned emperor in the half-ruined city of Rome, would have passed a profusion of people--beggars, slaves, artists, thieves, merchants and government officials dressed in a mix of styles from Persia, Greece and India; soldiers swaggering in polished armour; and traders from as far away as Spain and China.
According to an Arab chronicler named Abu al-Wafa Ibn Aqil, writing in Baghdad during the mid-eleventh century, the city was filled with palaces, gardens, fountains and mosques of exquisite beauty--as well as hospitals, schools and libraries. Along the Tigris, says Ibn Aqil, the rich built elegant residences, riding to and fro in small boats ‘in good trim . . . with beautiful finery and marvellous woodwork’. He spends pages describing the great suqs, or markets, and their busy streets set aside for shoemakers, flower vendors, tailors, moneychangers, swordsmiths, perfumeries and other merchants selling everything imaginable. One of these suqs, he says, was ‘unequalled for the beauty of its architecture’, with ‘tall buildings with beams of teakwood supporting overhanging rooms’. Another was known as ‘the meeting-place of learned men and poets’. Still others offered shops full of books and entertainments ranging from recitations of the Koran to fencing and wrestling shows.
Scholars, engineers, scientists and artists flocked to Baghdad from every corner of the empire, and were honoured and well paid. Many came bearing manuscripts, and the early years of the Abbasid period became a great era of translation. This project was made infinitely simpler when the first paper factory opened in Baghdad in 794, using a process the Arabs learned from a Chinese prisoner captured during the 712 conquest of Samarkand, in modern Uzbekistan. This invention would be passed on to Europe centuries later, just in time to provide late medieval scholars with an easy-to-make and inexpensive material on which to write out their own translations of ancient works.
As the translations and the originals began to stack up in the universities and libraries of Baghdad, al-Mamun ordered a museum and library complex to be built that became known as the House of Wisdom, the Bait al-hikma. Completed by 833, it became the most outstanding single repository of knowledge and scholarship since the great library in Alexandria: a place where scholars pondered the ancient writings and, as time went by, developed theorems, concepts and applications of their own.
By the second decade of the ninth century, just a generation after Kanaka’s arrival, a new and vibrant Arab intelligentsia were making breakthroughs in everything from medicine, chemistry and optics to a new philosophy of science that framed the pursuit of knowledge in terms of better serving God.
In the realm of time reckoning and astronomy, the Arabs first applied Greek and Indian ideas about measuring time to a practical need for their religion: when exactly they should kneel and pray, which Mohammed required all Moslems to do five times a day. This inspired early Arab astronomers to use and improve upon Greek instruments such as the astrolabe, sundial and globe to better calculate the angles of the sun at various times of day. Astronomers also advised architects throughout the Moslem world where to build mosques so that the faithful could follow another command of the Prophet--that they always face the direction of Mecca when they pray, whether they are in the Hindu Kush or on the Rock of Gibraltar.
Moslem astronomers and mathematicians also went to work refining the Islamic calendar. This calendar--whose year 1 began in our year AD 622, when Mohammed fled Mecca for Medina--was established by the second caliph, Umar, around AD 634. Years in the Islamic calendar are indicated with the abbreviation ah, which stands for the Latin anno hegirae, or ‘the Year of the Migration’. Since then it has been running at the standard lunar time of 354 days a year, drifting across the seasons to start on the same day every 325 years.
Each month in the Islamic calendar begins about two days after the new moon, when the first sliver of the crescent moon is sighted. Because the lunar month averages about 29 1/2 days, Umar arranged the twelve months of the Moslem year to alternate between 29 and 30 days:<
br />
Name
Let
Muharram
30
Safar
29
Rabi’u’l-Avval
30
Rabi’u’th-Thani
29
Jamadiyu’l-Avval
30
Jamadiyu’th-Thani
29
Rajab
30
Sha’ban
29
Ramadan
30
Shawal
29
Dhi’l-Qa’dih
30
Dhi’l-Hijjih
29
Most of these month names predate Islam, with some referring to seasons--suggesting that the Arabs’ calendar may have been lunisolar before Mohammed’s day. The second month, Safar, meaning ‘yellow’, originally came around in autumn when leaves were turning colour. Mohammed also designated four months that were sacred, when Moslems were forbidden to go to war or to conduct raids; of these, the ninth month, Ramadan, is the holiest, when Moslems are supposed to fast and abstain from sex during the daylight hours in order to learn self-discipline, and to concentrate on spiritual matters. Some believe the word Ramadan comes from the Arabic ramz, ‘to burn’, because the fast is supposed to ‘burn’ away one’s sins. In the Koran Mohammed writes:
As to the month of Ramadan in which the Koran was set down to be man’s guidance ... as soon as any one of you observeth the moon, let him set about the fast.
From this relatively simple early calendar Arab astronomers in the House of Wisdom and elsewhere worked to make the most precise lunar calendar possible. Their solution was a 30-year cycle of 360 lunar months, which is accurate against the true orbit of the moon to within a day of drift every 2,500 years. But this system requires frequent intercalations, with one day being added to the final month, Dhi’l-Hijjih, in the 2nd, 5th, 7th, 10th, 13th, 16th,
18th, 21st, 24th, 26th and 29th years of each 30-year cycle.
To facilitate this and other practical astronomical inquiries, Caliph al-Mamun ordered an observatory built in Baghdad in 829, and one soon after outside of Damascus. Astronomers also set up a network of observation points across the empire that allowed them to conduct experiments. One of these set out to determine the size and circumference of the world, which Arabs assumed was round. Taking measurements on a plain north of the Euphrates and near Palmyra, astronomers were able to calculate the width of a degree of the meridian,* coming up with 56 2/3 Arabic miles. This is just 2,877 feet wider than the actual degree.
*This refers to a measurement made by locating a meridian and moving north or south along it until one has moved exactly one degree of latitude.
One of the astronomers involved in the project of measuring the distance between two meridians was almost certainly Abu Jafar Mohammed ibn Musa al-Khwarizmi (780-850), perhaps the greatest of the scholars working at the House of Wisdom during the golden age, and the most influential mathematician on any continent during the early Middle Ages.* As famed among Arabs as Euclid and Ptolemy, and later respected by the Europeans of Roger Bacon’s day, al-Khwarizmi was probably born near the Aral Sea in modern Turkestan, called Khwarizmi in his era. Working in the city of Merv, south of the Aral Sea, he became famous enough to be summoned to Baghdad in 820 by al-Mamun, who appointed him ‘first astronomer’ and later head of the library at the House of Wisdom. An Arab version of what Europeans call a ‘Renaissance man’, al-Khwarizmi wrote on a dizzying number of subjects from mathematics and astronomy to geography and a history of the Arab caliphates. He also led three scientific missions to India and Byzantium to meet with scholars and collect manuscripts.
*His name means ‘Mohammed, the father of Jafar and the son of Musa, from Khwarizmi’.
He is best known, however, for being one of the first major scholars in the Arab world to use the accumulating store of knowledge from India, Greece and Persia to make his own discoveries. These include the invention of modern algebra. Indeed, the word algebra itself comes from one of al-Khwarizmi’s books, Kitab al-jabr wa al-muqabalah (Calculation by Restoration and Reduction). Later this became a standard textbook of mathematics in European universities until the sixteenth century. The word algorithm--algoritmus in Latin--comes from medieval Europeans’ use of al-Khwarizmi’s own name to refer to the study of mathematics.
Al-Khwarizmi wrote out the oldest surviving zij--set of astronomic tables--in the Arab world, much of it based on Indian charts possibly brought to Baghdad by Kanaka. This zij later made the journey to Spanish Cordoba and onwards to the rest of Europe, where a Latin translation made in 1126 became one of the most influential works on astronomy in medieval Europe.
Perhaps most important of all was a small booklet al-Khwarizmi penned in 825. Called Algoritmi de numero Indorum when it was later translated into Latin, this short treatise detailed something the great sage of Baghdad apparently picked up from reading Brahmagupta: the numerical system of the Indians--the nine symbols and a placeholder called sunya. Amazed by the usefulness of these simple symbols and of positional notation he demonstrated in his pamphlet their superiority to the Greek numbers then used in Baghdad, and to the cruder Bedouin numbers the Arabs had brought with them from the desert. At the time he wrote his booklet the ‘new’ Indian symbols looked something like this:*
*No one knows what the symbols looked like in Al-Khwarizmi’s booklet because no original has survived in Arabic. The only extant copies are Latin translations.
Later Arab mathematicians expanded on the system described in al-Khwarizmi’s pamphlet and on the Indians themselves to take the Hindu idea of sunya--the Arabs’ cifra, our zero--and use it not merely as a placeholder, but as a number like any other in certain calculations and equations. They also made a mathematical leap that the Indians did not, applying the system of positional notation to create decimal fractions--the first of which appear in an obscure book by an otherwise unknown Syrian mathematician named Abul Hassan al-Uqlidisi in 952 or 953. These discoveries made it possible just before the end of the first millennium of the Christian era to actually write out the number that represent the true solar year--365.242199 days--though as of yet no one had been able to come up with such an exact astronomic value. It also would have been written without the dot for the decimal point, which was added much later.
Al-Khwarizmi’s contemporaries in Baghdad were delighted with his little book. Used to a dizzying rush of new knowledge in this era of learning and scholarship, they quickly dropped the old methods of counting and embraced the new--which greatly accelerated the development of mathematical theory that would lay the foundation for modern science, including the reform of the calendar.
Scholars in Damascus to the west began using the new numbers just a few years later, but this invention took almost a century and a half to make the long journey to Spain, Sicily and other, more distant outposts of Islam. It took longer still to make the leap across the borders to a conservative Europe largely uninterested in new ideas, particularly those connected to a people they considered heathens in league with the devil.
Al-Khwarizmi was hardly the only genius at work in the Arab world during its glory years between the founding of Baghdad as the Abbasid capital in 763 and the final dissolution and fragmentation of the Islamic empire in the 1200s and 1300s. It is impossible to mention all of these, though a handful stand out above the rest in terms of the calendar. These include another denizen of the House of Wisdom born around the time of al-Khwarizmi’s death, Abu Allah Mohammed Ibn Jabir al-Battani (c. 850-929), known in Europe as Albategnius. In a book called On the Motion of the Stars he expounded on Indian trigonometric methods to show that the distance from the earth to the sun varies during the year, something we now know happens in part because the earth’s orbit is elliptic. Al-Battani also refined values for the length of the year by comparing it with calculations made by Ptolemy in 139. He came up with a figure that was 23 minutes too short--but that was because Ptolemy had placed his equinox a day late. H
ad Ptolemy been correct, al-Battani’s year would have been only half a minute short.
Half a century later another Arab astronomer, Abu ar-Rayhan Mohammed ibn Ahmad al-Biruni (973-1048), was born in central Asia. There he thrived despite the growing instability in the region as the Abbasid caliphate collapsed and its territories fragmented into shifting emirates ruled by local shahs and warlords.
Before the age of 30, in the midst of wars between rival kings, al-Biruni was able to make extensive observations of equinoxes and to travel to and fro taking highly accurate measurements of latitude. Also before turning 30--even as he was forced at times to go into hiding because of politics--he managed to write at least eight works. These included a treatise on timekeeping, a timeline of past events dated according to the Moslem calendar and arguments for and against the earth’s rotating on its axis, taking up the debate of Aryabhata versus later Indian astronomers.
Al-Biruni later became a diplomat for one rival shah and was imprisoned by another, though he was eventually allowed to continue his work as he followed an invading Moslem army into India. There he learned Sanskrit and studied every ancient text he could find, compiling his findings into a book called India. This offers a remarkably candid and critical analysis of Hindu mathematics and the siddhantas. In his late sixties al-Biruni wrote a study on the specific gravity of gems; at the age of 80 he wrote an alphabetical guide to 720 drugs, listing each according to their names in five languages.
The Calendar Page 17