From Salonica, City of Ghosts: Christians, Muslims and Jews, 1430-1950, by Mark Mazower (Vintage, 2006), pp. 26-27:
The Turks’ attitude to religion came as a pleasant relief to many Orthodox Christians. Held captive by the Ottomans in 1355, the distinguished archbishop of Salonica, Gregory Palamas, was surprised to find the Orthodox Church recognized and even flourishing in the lands under the emir. Prominent Turks were eager to discuss the relationship of the two faiths with him and the emir organized a debate between him and Christian converts to Islam. “We believe in your prophet, why don’t you believe in ours?” Muslims asked him more than once. Palamas himself observed an imam conducting a funeral and later took the opportunity to joust over theology with him. When the discussion threatened to overheat, Palamas calmed it down by saying politely: “Had we been able to agree in debate we might as well have been of one faith.” To which he received the revealing reply. “There will be a time when we shall all agree.”
As Byzantine power waned, more and more Orthodox Christians felt caught between two masters. Faced with an apparent choice between the reviled Catholics (their sack of Constantinople in 1204 never to be forgotten) and the Muslim Turks, many opted for the latter. Written off as an embarrassment by later Greek commentators, the pro-Turkish current in late Byzantine politics was in fact a powerful one for the Ottomans, who could be seen as protectors of Orthodoxy against the Catholics. The hope for political stability, the desire for wealth and status in a meritocratic and open ruling system, admiration for the governing capacities of the Ottomans, and their evident willingness to make use of Christians as well as Muslims explain why administrators, nobles, peasants and monks felt the allure of the sultans and why many senior Byzantine noble families entered their service. Murad II‘s grand viziers were well known for their pro-Christian sympathies; Murad himself was influenced by dervish orders which preached a similarly open-minded stance, and the family sheykh of the Evrenos family was reputed to be a protector of Christians. In the circumstances, it is not surprising why surrender seemed far more sensible an option than futile resistance against overwhelming odds, and why the inhabitants of Salonica themselves were known, according to at least one Byzantine chronicler, as “friends of the Sultan.”
In the second half of the fourteenth century, one Balkan town after another yielded to the fast-moving Ottoman armies; the Via Egnatia fell into their hands, and even the canny monks of Mount Athos submitted. Salonica itself was blockaded for the first time in 1383, and in April 1387, surrendered without a fight. On this occasion, all that happened was that a small Turkish garrison manned the Acropolis. The town’s ruler Manuel Palaeologue had wanted to resist, but he was shouted down by the inhabitants, and forced to leave the city so that they could hand themselves over. Manuel himself paid homage to the emir Murad, and even fought for his new sovereign before being crowned emperor.
Had the city remained uninterruptedly under Ottoman control from this point on, its subsequent history would have been very different, and the continuity with Byzantine life not so decisively broken. Having given in peacefully, Salonica was not greatly altered by the change of regime, its municipal privileges were respected by the new rulers and its wealthy monastic foundations weathered the storm. The small Turkish garrison converted a church into a mosque for their own use, and the devshirme child levy was imposed—at intervals Turkish soldiers carried off Christian children to be brought up as Muslims—which must have caused distress. But returning in 1393, Archbishop Isidores described the situation as better than he had anticipated, while the Russian monk Ignatius of Smolensk who visited in 1401 was still amazed by its “wondrous” monasteries.