[1] The siege culminated a lengthy campaign on the Ottoman side, which involved coordinated but independent manoeuvres by a large army and navy.

The Ottoman land campaign, which was the more challenging part, involved intimidating the ruler of Sinope into surrendering his realm, a march lasting more than a month through uninhabited mountainous wilderness, several minor battles with different opponents and finally the siege of Trebizond.

Only among the wild villages of Mani, in the southeastern Peloponnese, into whose rugged mountains no Turk ventured to penetrate, was there left any semblance of liberty.

William Miller quotes Kritoboulos as stating that Emperor David of Trebizond's "reluctance to pay tribute and the intermarriages with Hassan and the Georgian court provoked the Sultan to invade the Empire.

"[6] On the other hand, Halil İnalcık cites a passage from the 15th-century Ottoman historian Kemal Pasha-zade, who wrote:[7] The Greeks used to live on the coasts of the Black and the Mediterranean Seas in the good habitable areas which were protected by the surrounding natural obstacles.

[14] His brother and successor David is thought to have commissioned Michael Aligheri—and possibly the questionable Ludovico da Bologna—to travel to Western Europe in 1460 searching for friends and allies.

[15] But the most powerful and reliable ally of the Emperors of Trebizond was the ruler of the Aq Qoyunlu (or White Sheep Turkomen), Uzun Hasan.

The grandson of a princess of the Grand Komnenoi, Uzun Hasan had made the Aq Qoyunlu into the most powerful tribe of Turkmen by defeating their rivals the Black Sheep; he had heard of the beauty of the Emperor John's daughter Theodora Komnene (or Despina Khatun), and in return for her hand, Uzun Hasan pledged himself to protect her home city with his men, his money, and his person.

The city was deserted due to plague and likely to fall; John made his submission and agreed to pay an annual tribute of 2,000 gold pieces in return for Hizir freeing the captives he had taken.

[16] A tribute of 3,000 gold pieces each year must have proven too much for the revenues of the Empire because either John or David approached their relative by marriage Uzun Hasan about transferring the allegiance of Trebizond from the Ottomans to him.

[2] According to Doukas, as word of the Sultan's preparations circulated the inhabitants of places as far apart as Lykostomion (or Chilia Veche) at the mouth of the Danube, Caffa in the Crimea, Trebizond and Sinope, and the islands of the Aegean Sea as far south as Chios, Lesbos, and Rhodes, whether or not they had acknowledged his hegemony, all worried they would be his target.

He had written the ruler of Sinope, Kemâleddin Ismâil Bey, to send his son Hasan to Ancyra, and the young man was already there when Mehmed reached the city and received his overlord graciously.

[22] Mehmed made his interests quickly known: according to Doukas, he informed Hasan, "Tell your father that I want Sinope, and if he surrenders the city freely, I will gladly reward him with the province of Philippopolis.

[28] Doukas states that Mehmed led his soldiers across Armenia and the Phasis River, then ascended the Caucasus Mountains before reaching Trebizond.

Mihailović, on the other hand, states that the assassin was acting under the orders of Uzun Hassan and describes how the man was tortured for a week before he was executed.

[33] Meanwhile, Admiral Kasim Pasha had completed his work in Sinope and, assisted by a veteran seaman named Yakub, sailed to Trebizond.

Both Chalkokondyles and Kritoboulos state that his Grand Vizier, Mahmud Pasha Angelovic, arrived one day before the Sultan and began the negotiations for surrender.

The walls of Trebizond were massive and elaborate; David expected his relative Hassan Uzun to arrive at any moment to relieve the siege, perhaps his ally, the King of Georgia, or perhaps even both.

[39] In the end, Emperor David Megas Komnenos chose to surrender his city and empire and trust that Sultan Mehmed would be merciful.

Both Stephen Runciman and Franz Babinger note this date was the 200th anniversary of Michael VIII Palaiologos' recapture of Constantinople from the Latin Empire.

"[45] Mehmed converted the Panagia Chrysokephalos cathedral in the center of the city into Fatih Mosque, and in the church of Saint Eugenios he said his first prayer, thus giving the building its later name, Yeni Cuma ("New Friday").

One tells how the citizens, expecting an army to arrive before dawn to force the Sultan to lift the siege, agreed to surrender at cock-crow.

[51] According to Chalkokondyles, Mehmed appointed Kasim Pasha to be governor of Trebizond and had Hizir accept the submission of the villages around the city and in Mesochaldia, home of the Kabasites clan.

Although Chalkokondyles implies that these communities quickly acquiesced to Ottoman rule,[52] Anthony Bryer has found evidence that some groups resisted their new Muslim overlords for as long as ten years.

[55][better source needed] Pope Pius II sought to rescue Trebizond, yet by his death in 1464, no Christian nation had undertaken a Crusade against the Ottomans.