The Ottoman Interregnum — the civil war that followed Bayezid's defeat — lasted from July 1402 to July 1413. Four of Bayezid's sons claimed the sultanate: İsa, Musa, Süleyman, and Mehmed, with Mustafa appearing later as a fifth claimant. Timur had nominally confirmed Mehmed Çelebi as sultan after Ankara, but confirmation by a foreign conqueror meant little in practice. Each prince controlled a portion of the empire's territory and its soldiers. Süleyman held Rumeli — the European provinces, including the Ottoman capital of Edirne — and concluded the Treaty of Gallipoli with the Byzantine regent John VII Palaiologos in 1403, giving Thessaloniki and Marmara coastal territories back to Byzantium in exchange for Byzantine diplomatic support. Manuel II, still traveling in western Europe at the treaty's signing, subsequently endorsed it. This arrangement made the Byzantines Süleyman's ally — and therefore, in Musa's eyes, his enemies.

Süleyman's position crumbled faster than anyone anticipated. Despite defeating Musa at the Battle of Kosmidion in June 1410, he could not hold his supporters. His behavior — erratic, reportedly dissolute — alienated the soldiers and officials who had backed him. When Musa returned to challenge him again in early 1411, Süleyman's men simply switched sides. He was captured while trying to flee. On 17 February 1411, Süleyman Çelebi was given to Musa's bodyguard, Koyun Musasi, and strangled. The death of a sultan by strangulation — a method the Ottomans would later make grimly routine in succession struggles — was shocking but not unprecedented. What followed was Musa's consolidation of power over Ottoman Europe, and with it, a settling of accounts. The Byzantines, who had backed the dead man, waited to learn the price.

Musa Çelebi, now holding the European portion of the Ottoman Empire, moved against his enemies. Constantinople was among them. Manuel II had supported Süleyman; that made the Byzantine emperor a target of Musa's consolidation campaign. The siege that followed in 1411 was brief and, in military terms, inconclusive — Musa laid siege to the city but could not seriously threaten its walls. Constantinople's Theodosian defenses, which had held for decades against far more sustained efforts, were not going to fall to a punitive expedition mounted under political pressure. The walls along the peninsula's landward side, massive and triple-layered, made a quick assault impossible. A prolonged siege, however, was exactly what Musa could not afford: his hold on power was not yet secure, and other brothers were circling.

What ended the siege was not Byzantine military action but Byzantine diplomacy. Manuel II, watching the Ottoman civil war from inside his walls, reached out to Mehmed Çelebi — Musa's brother and rival, who controlled Anatolia. Mehmed accepted. The new alliance between Mehmed and Byzantium effectively turned Musa's rear threat into a vice. Musa found himself squeezed between Byzantine Constantinople to his west and Mehmed's Anatolian forces pressing from the east. The siege was lifted. Musa's hold on Ottoman Europe would not survive the reversal: he was eventually defeated by Mehmed at the Battle of Camurlu on 5 July 1413 — strangled, as his brother Süleyman had been, by the bodyguard of the man who supplanted him. Mehmed I emerged as the undisputed sultan and closed the book on the Interregnum. Constantinople had, once again, survived by outlasting the man who threatened it.

The siege of 1411 is among the shortest and least studied of the many assaults Constantinople endured. It lasted weeks rather than years and produced no decisive battle, no famous last stand. But it belongs to a pattern that defined the city's survival across centuries: the ability to withstand pressure long enough for the attacker's circumstances to change. Where Bayezid had kept up the blockade for eight years only to be destroyed by Timur, Musa maintained his siege for weeks before being outmaneuvered by his own family. The city on the Bosphorus did not need to win. It needed to endure. The Theodosian Walls, the Golden Horn, the sea lanes it could still use — these were the instruments of endurance. The people inside simply had to hold, and hold they did, while the world outside rearranged itself around them.