A rising imperial power that conquered Constantinople and became central to late medieval European politics.
The Ottoman Empire grew from a Bithynian frontier beylik into the power that ended Byzantium: Osman's ghazi band (c. 1299) to Orhan's Bursa and the Gallipoli crossing (1354), Murad I's Adrianople and the Battle of Kosovo (1389), Bayezid I's empire wrecked by Timur at Ankara (1402) and rebuilt within a generation — to Mehmed II's conquest of Constantinople in 1453.
Its medieval machinery — the devshirme levy and Janissaries, timar cavalry, ghazi legitimacy fused with Perso-Islamic statecraft, and Europe's best siege artillery — made it by 1453 the heir of Rome in its conquerors' own style: Mehmed as Kayser-i Rûm, Istanbul as the empire's new head.
The Seljuk sultanate of Rum's collapse under Mongol suzerainty left western Anatolia to ghazi frontier-lordships; Osman's, facing Byzantine Bithynia, was among the smallest and best-placed — raiding rich borderlands, absorbing warriors, dervishes, and defectors, its founding legend (Osman's dream of a world-tree) written later but its opportunism contemporary. The victory at Bapheus (1302) announced it; the long blockades did the work.
Orhan (c. 1324–1362) converted band to state: Bursa starved out (1326) as capital, Nicaea (1331) and Nicomedia (1337) following after Pelekanon beat the last imperial relief; the first coins, medreses, and standing infantry; marriage into the Byzantine civil wars (Theodora Kantakouzene) — and through them Thrace's roads learned, until the earthquake-breach at Gallipoli (1354) gave the Ottomans their permanent European gate.
Murad I (1362–1389) made Rumelia the empire's centre: Adrianople taken (c. 1369) and made capital Edirne; the Maritsa victory (1371) shattering the Serbian lords of Macedonia; vassalage webs over Bulgaria, Byzantium, and Serbia — and the Battle of Kosovo (1389), where sultan and prince Lazar both died and Ottoman suzerainty over Serbia hardened. The instruments matured with the conquests: the Janissaries raised from prisoner-levy and then devshirme, the kapıkulu household army, timar grants binding cavalry to conquered land.
Bayezid I "the Thunderbolt" pushed both ways at once — the beyliks annexed, Constantinople blockaded (1394–1402), the Nicopolis crusade destroyed (1396) — until Timur's invasion caught the over-stretched sultanate at Ankara (1402): army defected, sultan caged, beyliks restored, sons at war. The Interregnum (1402–1413) was the empire's near-death; Mehmed I's victory and Murad II's long consolidation (Varna's crusade crushed 1444, second Kosovo 1448) proved the structure — devshirme state, not steppe confederacy — could regrow its head.
Mehmed II inherited (1451) a project prepared: the Bosphorus cut by the fortress of Rumeli Hisarı (1452), Urban's great bombard cast, the fleet portaged over Galata's hill into the Golden Horn when the chain held. The fifty-three-day siege ended before dawn on 29 May 1453 — the walls breached where cannon had worked for weeks, Constantine XI dead in the fighting, three days' sack, and then reconstruction: Hagia Sophia a mosque, the patriarchate reappointed (Gennadios enthroned by the sultan), the city repopulated by decree into an imperial capital again.
The conquest closed the medieval Mediterranean's central question and opened the Ottoman imperial age: Serbia and the Morea absorbed (by 1460), Trebizond's last "Roman" empire taken (1461), Kayser-i Rûm added to sultan and ghazi in the titulature — the medieval frontier-band now running Rome's city, taxing its trade, and codifying (Mehmed's kanunname) the fratricide-succession and slave-administration that would rule three continents.
The Ottoman formula fused three inheritances: Turco-Mongol dynasty (the house of Osman alone throne-worthy, succession by contest among sons — codified as legal fratricide), Perso-Islamic administration (vizierate, chancery, kadi courts applying sharia and sultanic kanun), and the ghazi frontier (holy-war legitimacy shared with dervish orders and march-lords like the Evrenosoğulları).
Its distinctive engine was the kapıkulu — the sultan's slaves: devshirme boys from Christian villages trained into Janissary infantry and palace administrators, loyal to the dynasty against the Turkish aristocracy; beside them the timariot sipahis, holding revenue-grants for cavalry service, tied conquest to cultivation. Non-Muslim communities ran themselves under their clergy in return for the cizye tax — the arrangement later formalised as millets — making the empire, from birth, a machine for governing diversity.
Osman I, c. 1299–1324 — the eponym: dream, band, and Bapheus.
Orhan, c. 1324–1362 — Bursa, Nicaea, the first institutions, Gallipoli.
Murad I, 1362–1389 — Edirne, the Maritsa, Kosovo: Rumelia made the base; the Janissaries founded.
Bayezid I, 1389–1402 — Nicopolis's victor, Constantinople's blockader, Ankara's prisoner.
Mehmed I, 1413–1421 — the Interregnum's winner and re-founder.
Murad II, 1421–1451 — Varna and second Kosovo; the consolidator who twice abdicated.
Mehmed II the Conqueror, 1444/1451–1481 — 1453; the imperial codifier.