Alba Iulia is a city in Alba County, Transylvania, Romania, located on the Mureş River. Between 1541 and 1690 it was the capital of the Principality of Transylvania. The city is historically important for both Romanians and Hungarians.
Four villages are administered by the city: Oarda (Alsóváradja), Pâclişa (Poklos), Miceşti (Ompolykisfalud) and Bărăbanţ (Borbánd).
The modern city is located near the site of the important Dacian political, economic and social centre of Apulon, mentioned by the ancient Greek geographer Ptolemy and believed by many archaeologists to be the Dacian fortifications on top of Piatra Craivii. After the southern part of Dacia became a province of the Roman Empire, the capital of the Dacia Apulensis district was established here, and the city was known as Apulum. Apulum was one of the largest centers in Roman Dacia and the seat of the XIII Gemina Legion.
In the 9th century, the city was mentioned under the name of Belgrad or Belograd ("White Castle" in Slavic languages). The Gesta Hungarorum mention a ruler named Geula, Gyula, or Jula, who had discovered the city and made it the capital of his dukedom during 10th century. Following the establishment of the Catholic Transylvanian bishopric after Stephen I of Hungary adopted Catholicism, the first cathedral was built in the 11th century. The present (Catholic) cathedral was built in the 12th or 13th century. In 1442, John Hunyadi, Voivod of Transylvania, used the citadel to make his preparations for a major battle against the Ottoman Turks. The cathedral was enlarged during his reign and he was entombed there after his death.
As Gyulafehérvár, Alba Iulia became the capital of the Principality of Transylvania in 1541, a status it was to retain until 1690. The Treaty of Weissenburg was signed in the town in 1551. It was during the reign of Prince Gabriel Bethlen that the city reached a high point in its cultural history, with the establishment of an academy. Further important milestones in the city's development include the creation of the Batthyanaeum Library in the 18th century and the arrival of the railway in the 19th century.
In November of 1599, Michael the Brave, Voivode of Wallachia, entered Alba Iulia following his victory in the Battle of Şelimbăr and became Voivode of Transylvania. In 1600 he gained control of Moldavia, thereby uniting the three principalities under his rule until his murder in 1601 by Giorgio Basta's agents. This was the first unification of the three Romanian-populated principalities of Wallachia, Moldavia, and Transylvania, lasting for a year and a half. In 1918, tens of thousands of Romanians (the exact number is disputed between Romanian and Hungarian historians) and representatives of the Transylvanian Saxons and other minorities of Transylvania gathered in Alba Iulia on 1 December, now commemorated as the National Day in post-communist Romania, to hear the proclamation of the union of Transylvania with the Kingdom of Romania. In 1922, Ferdinand of Romania was symbolically crowned King of Romania in Alba Iulia in an act which mirrored the achievement of Michael the Brave.
- The main historical area of Alba Iulia is the upper city, developed extensively by Charles VI of the Holy Roman Empire, in honour of whom the Habsburgs renamed the city Karlsburg. The upper city's fortress, with seven bastions in a stellar shape, was constructed between 1716 and 1735 by Giovanni Morando Visconti, using the Vauban system—the largest of this kind in south-eastern Europe.
- Inside the fortress is the Roman Catholic Cathedral (the most representative building for the Medieval Gothic style in Transylvania), the Batthyaneum library, the Roman Catholic Bishop's palace, the Orthodox Cathedral, Babylon Building (National Museum of Unification), Union Hall, Apor Palace, the Princely Palace, and the University of Alba Iulia.
- Built in the 13th century, the Roman Catholic Cathedral is considered to be an important monument of early Transylvanian medieval architecture. The tomb of John Hunyadi is located here, as is that of the Polish-born Isabella Jagiełło, Queen of Hungary.
- The Bathyaneum library is a late church, built in Baroque style. In 1780, Ignác Batthyány, bishop of Transylvania, adapted the inside of the establishment for its present use as a library. It is famous all over the world for its ample series of manuscripts, incunabula and rare books, such as Codex Aureus (9th century), also known as the Lorsch Gospel, containing the Gospel of Mark and Matthew, David's Psalms, Codex Burgundus (15th century), Biblia Sacra (13th century), the Pentateuch from Orăştie (1850), Şerban Cantacuzino's Bible, and the New Testament from Balgrad (1648). The first astronomical observatory in Transylvania was founded here in 1792.
- The Reunification Cathedral was built between 1921 and 1923, following plans drawn by the architect D.G. Ştefănescu, executed by the engineer T. Eremia. Constantin Petrescu painted the fresco in traditional iconographic style. The first monarchs of unified Romania, King Ferdinand I and Queen Marie, were crowned in the cathedral on 15 October 1922.
- The National Museum of Unification in Alba Iulia is located in the Babylon Building. It was originally built for military purposes in 1851–1853 and transformed into a museum in 1887. The museum exhibits over 130,000 pieces of priceless works, organized chronologically: first a prehistory section, then Dacian–Roman and feudal sections, followed by the great battles with the Turks, the Revolution of 1848, the Unification of the Principalities in 1859, World War I, the Union of Transylvania with Romania, and so forth. In its two floors with more than a hundred rooms are housed the basic exhibition, the warehouse, the library, and the restoration laboratories. The Unification Hall, also belonging to the National Museum, was opened in 1895 as Military Casino of the Garrison in Alba Iulia; it retains historical significance from its having hosted, on 1 December 1918, the rally of the 1228 Romanian delegates from all Transylvania, who determined the province's union with Romania.
- Apor Palace is situated near the Bathyaneum Library. It belonged to the Prince Apor, and was built in the second half of the 17th century. At the beginning of the 18th century it was the residence of the Austrian army leader Prince Steinville. The palace was renovated in 2007.
- The Princely Palace (Palatul Principilor) was Michael the Brave's residence during the first political unification of the Romanians in 1600. Foreign chronicles pictured it as an extremely luxurious building, richly adorned with frescos and marble stairs; however, it was destroyed in Ottoman and Tatar invasions. During the rule of princes Gábor Bethlen and George II Rákóczi the second palace was restored, but not to its previous condition. From 1700 the building was used as a barracks.