historic eastern European region. After forming part of Hungary (11th–16th century), it was an autonomous principality within the Ottoman Empire (16th–17th century) and then once again became part of Hungary at the end of the 17th century; later it was incorporated into Romania (1918–20). The region, whose name first appeared in written documents in the 12th century, covered a territory bounded by the Carpathian Mountains on the north and east, the Transylvanian Alps on the south, and the Bihor Mountains on the west. The neighbouring regions of Maramureș, Crișana, and Banat have also, on occasion, been considered part of Transylvania.

Having formed the nucleus of the Dacian (Dacia) (Getic) kingdom (flourished 1st century BC–1st century AD) and the Roman province of Dacia (after AD 106), Transylvania was overrun by a succession of barbarian tribes after the Roman legions withdrew about AD 270. Thereafter the Romanized Dacian inhabitants either moved into the mountains and preserved their culture or migrated southward. The area then was repopulated by peoples from the Romanized lands south of the Danube River or from the Balkans. The Magyars (Hungarians (Hungarian)) conquered the area at the end of the 9th century and firmly established their control over it in 1003 when their king Stephen I, according to legend, defeated the native prince Gyula. Administration was consolidated by the settlement, probably as frontier guards, of the Székely (Szeklers, a people akin to the Magyars) and the Saxons (Germans). The Magyars encouraged the political and economic development of the region. Despite the interruption caused by the Mongol invasion of 1241, Transylvania (while remaining part of the Hungarian kingdom) evolved during the following centuries into a distinctive autonomous unit, with its special voivode (or governor), its united, although heterogenous, leadership (descended from Szekler, Saxon, and Magyar colonists), and its own constitution.

When the Turks decisively defeated Hungary at the Battle of Mohács (1526), Transylvania effectively became independent. Its voivode John (János Zápolya), who was elected king of Hungary (November 1526), engaged Transylvania in a 12-year war against Ferdinand I, the Habsburg (Habsburg, House of) claimant to the Hungarian throne. Afterward Hungary was divided between the Habsburgs and the Turks, and Transylvania was transformed into an autonomous principality that was subject to Turkish suzerainty (1566).

During the next century Transylvania—ruled by the Báthory dynasty (1570–1613, with interruptions), István Bocskay (Bocskay, István) (reigned 1605–06), Gábor Bethlen (Bethlen, Gábor) (reigned 1613–29), and György Rákóczi (Rákóczi, György, I) I (reigned 1630–48)—played off the Turkish sultan against the Habsburg emperor to retain its independent status. It emerged from a series of internal religious struggles, accompanied by Habsburg intervention, as a power of international importance, a defender of Hungarian liberties against Habsburg encroachments, and a bulwark of Protestantism in eastern Europe.

During the reign (1648–60) of György Rákóczi II, the Turks, trying to curb Transylvania's growing power, stripped it of its vital western territory and made the obedient Mihály Apafi its prince (1662). Shortly afterward, the Turks were defeated before Vienna (1683). The Transylvanians, their land overrun by the troops of the Habsburg emperor, then recognized the suzerainty of the emperor Leopold I (1687); Transylvania was officially attached to Habsburg-controlled Hungary and subjected to the direct rule of the emperor's governors. In 1699 the Turks conceded their loss of Transylvania (Treaty of Carlowitz); the anti-Habsburg elements within the principality submitted to the emperor in 1711 (Peace of Szatmár).

During the succeeding century the pressure of Roman Catholic and bureaucratic rule gradually undermined the distinctive character of Transylvania. A strong Magyar movement, overshadowing the declining influence of the Szekler and Saxon nobles, urged the abandonment of the principality's separate administration and integration with Hungary. Consequently, during the Hungarian Revolution of 1848 (1848, Revolutions of), the Magyars of Transylvania identified with the insurgents. The Romanian peasantry, which had been developing its own national consciousness and agitating for more extensive political and religious liberties, took a stand against the Magyars and swore allegiance to the Habsburgs. When the Habsburgs reasserted their control over Hungary, Transylvania was separated from Hungary and transformed into a Habsburg crown land, subject to strict, absolutist rule. Subsequently, it was reabsorbed into Hungary (1867).

When Austria-Hungary was defeated in World War I, the Romanians of Transylvania in late 1918 proclaimed the land united with Romania. In 1920 the Allies confirmed the union in the Treaty of Trianon (Trianon, Treaty of). Hungary regained about two-fifths of Transylvania during World War II (Vienna Award; August 1940), but the entire region was ceded to Romania in 1947.