From The Making of Eastern Europe: From Prehistory to Postcommunism, by Philip Longworth (Lume Books, 2020), Kindle pp. 302-305:
There had been a good deal of peaceful interchange as well as fighting between Byzantium and the Ottomans in the decades preceding 1453; and not a little intermarriage. Mehmet’s own ancestors included Byzantine Christians. Besides he entertained considerable respect for some aspects of the Byzantine tradition; he was invited to think of himself as ‘Emperor of the Romans’, like the Byzantine Emperors of old, and came to believe that he could unite all Christendom under his rule. More immediately he used certain Byzantine institutions as models for the system he set up to run his Empire. Thus the Byzantine fief seems to have been the inspiration of the sipahi system; Byzantine offices, taxes and even ceremonials became bases for Ottoman administrative and court practices, and certain posts, particularly those involving foreign affairs, became almost a monopoly of Greeks. This is not to suggest, however, that much about the new regime was not alien and burdensome.
The Ottoman state was run by a system of slavery, even though the Sultan’s slaves constituted an administrative and military elite. Furthermore, the Turks took an irregular levy of children (devshirme) from their subject Christian population and made Muslims of them, even though they also trained them for their service and set them on ladders of opportunity which enabled them to reach the highest offices of state. Furthermore, Christians were made to feel their inferiority. They were forbidden to wear green or to paint their houses in bright colours, forbidden to ride horseback in the presence of Muslims, and restricted in the number and the height of their churches. On the other hand there was freedom of worship; non-Muslims were not obliged to do military service; and they were largely subject to their own justice within their own religious millets, of which by far the largest was the Orthodox, administered by the Patriarchate of Constantinople whose latest incumbent was invested in office by the Sultan himself. The Great Church was largely in captivity, but it retained most of its autonomy. The monasteries of Mount Athos were not disturbed, and the Turks did not distract the monk Gabriel of Rila from his life’s work, a vast compilation of the sayings of St John Chrysostomos.
The Ottoman Turks also breathed new life into decrepit Byzantine cities and above all into Constantinople which they called Istanbul. Christians, Muslims, Armenians and Jews were brought from all over the Empire and settled there. Hence the population which had shrunk to about 10,000 in the immediate aftermath of its fall increased by as much as tenfold within thirty years. Most came voluntarily recognising opportunity or responding to concessions, though some were forcibly resettled; and huge building and rebuilding projects were soon under way. Water supplies, sewage disposal, street-paving and street furniture were soon renewed or supplied for the first time; ruined structures were rebuilt, others restored and new palaces, fountains, public baths and hospitals erected. Also a great bazaar – for the Ottomans had long recognized the importance of commerce.
In the Balkan countryside Ottoman domination replaced uncertainty and periodic anarchy with an orderly system that did not at first always unduly disturb existing social relationships. Local lords who submitted to the sultan were generally left in possession of their estates in fief provided they served the Ottomans as loyal vassals. They were encouraged to convert to Islam and embrace Ottoman culture, of course, but pressures to do so tended to be applied gradually over a period of two or three generations, by which time many had gravitated naturally to the ways of the new elite. Lower down the scale peasants could gain privileges such as certain tax exemptions by serving as military auxiliaries or local police; most monasteries that had not earned the Sultan’s displeasure continued in the possession of most of their estates; and the populations of some regions, notably the heretical Bogomils of Bosnia, positively welcomed the Turks.
In two other respects the Ottoman system can be regarded as superior to some others in the Europe of the time. It was unequivocal about the ultimate ownership of property belonging to the state, eliminating powerful lordships, bases of individual power which could be exercised capriciously; and it did not permit the military class to become too numerous. Christian servicemen surplus to requirements were reduced in status and lost their privileges. This was not the case in Poland and Hungary, where, as we have seen, a swollen nobility and the virtually unrestricted power of lords were to be conducive to great harm. Furthermore the Turks provided security for the great majority of the Balkan population to live in tranquility in accordance with a familiar culture. By uprooting and changing Byzantine institutions, it has been said to have decapitated Byzantine high culture. On the other hand, as we have seen, Byzantine civilization had made some impression on the Turks themselves; and its cultural legacies, to both Eastern and Western Europe, were particularly rich.