Time for a quick note from sunny Spain: Seville to be precise.
The major sights here in Andalusia are the remaining great Islamic buildings such as the Alhambra, Mesquita and Giralda in Granada, Cordoba and Seville respectively. There is no question that these are masterpieces of architecture and that the Moorish civilisation that built them was advanced and cultured. Add to that the philosophers such as Moses Maimonides and Averroes, who both hailed from Cordoba, and one wonders how it was all lost. The answer is that the Moors split into a patchwork of small states and the more united Christians could pick them off one by one. Once Aragon and Castille joined together under Ferdinand and Isabella, even Granada could hold out no longer, falling in 1492.
But the question that I found myself asking is why was it that the Islamic invaders of the Eastern Roman Empire could immediately form an advanced civilisation while the invaders of the Western Empire, such as the Goths, Franks and Saxons took five hundred years before they achieved a comparable level. After all, both sets of invaders had started off as nomads on the fringes of the Empire. The silly but traditional answer is that Islam was somehow more "enlightened" than the Christianity of the western invaders whose religion left them in the Dark Ages. Clearly this is rubbish as the Christian states were eventually able to overtake the Caliphate in both technology and culture. But the fact remains that Islamic civilisation got a head start. Why?
I´ve been reading Jared Diamond´s Guns, Germs and Steel over the holidays. I´ll have some critical comments to make about it later but inspired by him, I think I can answer the problem I set out above. Two answers present themselves.
First, the Western invaders were made up a of several tribes that each over ran the same area. This meant that individual cities were often sacked many times as the Vandals, then the Goths, then the Franks and finally the Huns all arrived from the East. It meant the damage to infrastructure and society was much greater than in the East. There, Islamic invaders were united so there was only a single invasion that was able to capture territory with its infrastructure intact. The Arabs just supplied a new ruling class. This had initially happened in the West too where Theodoric the Goth ruled over Roman senators, but further invaders destroyed this.
Second, the cultural heart of the Roman Empire was the East and not the West. All academic work, maths, philosophy and medicine was available only in Greek. It was the Greek speaking part of the Empire that the Arabs took over and hence it was easy to find Greek speakers to transmit knowledge to them. In the West, the language was Latin which had no scientific tradition and so the invaders were not going to be exposed to classical learning. Even the Western church was Latin based and so it could only preserve literature in that language.
Thus, the combination of the Arab invaders taking over in one fell swoop, combined with their occupation of the intellectual heartland of the Roman Empire, including Alexandria, meant they were much more able to continue a high level of civilisation than the warring tribes flooding piecemeal into the west.