Alba Carolina fortress seen from above has the shape of a seven-pointed star. Under the star lie two more fortresses, one over another: the Roman camp and the medieval fortress. Below, we build the star bastion by bastion.
the terrace the town today
Three fortresses in one
The fortress with seven corners
From a plane, the fortress at Alba Iulia looks less like a fortress than a star drawn on the ground, with seven sharp points. The points are bastions: seven of them, joined by brick walls, ringed with deep ditches. The star has a purpose: each point guards its neighbouring wall with flanking fire, so the straight wall of the old fortresses died here, replaced by geometry.
Under the star hide two more fortresses, one over another: the Roman camp of Legio XIII Gemina and the medieval fortress with its cathedral. Every fortress raised here swallowed the older one. We open the terrace together, layer by layer: on the left you see the years and the layer you are in.
Where we build the star
Alba Iulia, Alba county, on the Mureș valley: the high terrace where the Romans set their camp almost two thousand years ago. The map below takes you from the country to the fortress.
After the conquest of Dacia (106), Rome set a whole legion here, XIII Gemina: a square of walls with four gates, the main road north to south, the headquarters in the middle. At first it was earth and timber; around 138 it turned to stone. How big was it? The reckonings disagree: 480 by 432 metres on today's record, 420 by 420 on an older one. In the 3D section you see both rectangles, so you know the measure is disputed.
Two towns grew beside the square: one at Partoș, raised to colonia under Commodus, another by the camp, raised to municipium under Septimius Severus. An inscription of the year 250 names a third town, Colonia Nova Apulensis, but nobody knows which of them it was. And the legion's bricks survive with their stamps: 123 roof tiles stamped LEG XIII GEM, found in 2021–22 on Șaguna street, some with people's names: Aurelius Enthimus, Flavius Martinus.
The camp south gate, porta principalis dextra. Photo: Saturnian, public domain, via Wikimedia Commons.
Middle layer · Bishops and princes
Then a wall on the Roman square
After the Romans left, the place neither emptied nor stayed a town the whole time: traces of dwelling from the 4th–6th centuries, then the 8th–9th, then the 10th. The medieval fortress rose on the Roman square, reusing its walls, and inside it grew St Michael's cathedral. After the Mongol raid of 1241, the campaign of today's cathedral began on the site: the masonry contracts of 1 November 1287 and 31 May 1291 survive in the archive, with the west portal of their time.
Alba was a bishop's seat — the year 1009 is tradition, the foundation charter is lost — and a seat of Transylvanian princes, from the mid-16th century to late in the 17th. The medieval walls stood until the Austrians decided they wanted something else instead.
The lesson · Ballistics made stone
Why it is no longer square
A straight wall has one weakness: at its foot lies a dead angle, where defenders above cannot shoot. The Italians found the cure in the 1500s: corners jutting outward, the bastions, from which gunners fire along the neighbouring wall, into the flank of whoever comes near. The Frenchman Vauban brought the system to perfection, and General Eugene of Savoy promoted it in Transylvania.
Look at the star in the 3D section: each point covers the wall beside it, and the ravelins in front add one more layer to cross. That does not mean every patch of ground could be seen perfectly, only that the man who reached the wall stood in the path of guns fired from the side. The ditches help too: 25 metres at the great one, 15 at the ravelins, 12 at the counterguard.
The building site · Visconti, 1715
A building site the size of a town
The plan was drawn by the Italian Giovanni Morando Visconti in 1714, and the foundation stone was laid on 4 November 1715, at Emperor Charles VI's bastion. Visconti died of plague in 1717 and lies in the Catholic cathedral; de Quadri and von Weiss carried the works on in stages, broadly until 1738. The city hall admits the works were never definitively finished.
What did it cost, and how many laboured? The municipal pages say over 20,000 Romanian peasants and some 2,000,000 gulden — but no old ledger has been published to check them, so the reckonings stay reported, not proven. What we know for certain is the material: bastions of brick packed with earth, gates of cut stone.
Gate III, the grand entrance: cut stone and statues. Photo: Ciprian.lazar, CC BY-SA 4.0, via Wikimedia Commons.
The star · Seven names
The seven corners, by name
In 1736 the bastions were given names, from Gate III leftwards, clockwise: Eugene of Savoy, Steinville (later St Stephen), Holy Trinity, St Michael, St Carlo Borromeo, St Elizabeth and St Capistrano (later Transylvania). All run to much the same measure: sides of 110–120 metres, height of 10–12 metres, points outward.
Two of them carry a memory from before the star on their backs: on the Eugene of Savoy and St Stephen bastions, Prince Gabriel Bethlen's old works stand in for raised cavaliers. And the points were dressed with statues on stone platforms. Between bastions, the 100-metre brick curtain joins the star.
The entrances · East–west
Six gates, not seven
The fortress is entered through six gates, three on each side, east and west, one on every defensive line. Four have richly sculpted facades. Gate III is the grand entrance, between the Eugene of Savoy and Capistrano bastions, with the equestrian statue of Charles VI. The statue alone cost 40,000 florins — the museum's reckoning, not the fortress's price.
Gate II was pulled down in 1937 and rebuilt from old photographs. And Gate VII is a troop passage reopened for visitors, not a gate like the others: that is why we count it separately. The gate route joins the civic centre to the western quarter today.
Baptism of fire · 26 March – July
Once attacked, never taken
The star was tested a single time. In 1848 the garrison disobeyed the government of Kossuth, and in 1849 the Hungarian army ringed the fortress: the siege began on 26 March, with some 8,000 men on Visit Alba's reckoning, and lasted into late July. The heavy bombardments fell on 2 April and 23–24 June, when Bem's troops arrived too.
The fortress held. The siege's daily journal is kept at the Batthyaneum Library, and the war papers in the Vienna archives. Nobody has attacked it since: the only trial in its 300 years of life.
The Trinity bastion brick wall. Photo: Pudelek, CC BY-SA 4.0, via Wikimedia Commons.
The 20th century · The hall and the crown
The Union Hall and the new cathedral
On 1 December 1918 the delegates gathered in the Union Hall — then the officers' casino, inside the walls — while the crowd stood on Horea's Field, outside. The photographer Samoilă Mârza stayed with the crowd: his pictures show the field, not the hall. The assembly's story is told by the page Alba Iulia 1918; here we care about the stones.
The new stone is the Coronation Cathedral, raised in 1921–22: on 15 October 1922 the service was held inside, and the crowning under a canopy, before the bell tower. Ferdinand set the steel crown on his own head, then crowned Maria.
Today · 70 hectares
The star to visit
Today's fortress spreads over just above 70 hectares — the 110 hectares sometimes named are the extent drawn on the plan, not the one built. All the walls together pass 12 kilometres in length. Between 2007 and 2013 the restoration swallowed over 210.8 million lei, and the east ditch is a building site again, from May 2025 to May 2027.
The ditch route and the gate route are free and open at all hours; the museums take separate tickets. And on the UNESCO list the fortress is not inscribed: the historic core sits on the waiting list since 1 March 1991, under the old French name “Le noyau historique de la ville d'Alba Julia”. For current hours and tickets, see the tourism page.
Both cathedrals at dusk: the Coronation one (left, 1921–22) and St Michael (right). Photo: Tudor evi, CC BY-SA 3.0 RO, via Wikimedia Commons.
Choose the layer
Jump to the layer that interests you; the 3D section shows it.
Geometry: how the star shoots
The star's secret sits in a single sentence: no wall defends itself alone. Each bastion juts out like a spearhead, and the gunners on its flanks fire along the neighbouring wall. The man who reaches the wall's foot, in the dead angle below, stands in the path of guns fired from the side. That is why the curtain wall leans at 80 degrees, thinning from 2.50 metres at the base to 2 metres above: the earth behind presses, the wall holds.
The defensive layers are three: the enceinte with its seven bastions, the ravelins before it (sides of some 90 metres, with 6-metre reduits on two of them) and the outer zig-zag counterguard. Between them, the ditches: 25 metres at the great one, 15 at the ravelins, 12 at the counterguard. And the flanks, at Alba Iulia, have no casemates like other Vauban works: tenailles guard them, two islands of earth and masonry 4 metres high, 50 metres apart, between which the artillery fires undisturbed.
For the classroom: draw on paper a bastion like a spearhead and a straight wall beside it. Set a dot at the wall's foot — you are the besieger. Now rule a line from the bastion's flank to the dot: it hit you. Move the bastion further off and see when you escape.
People: who laid hands on stone
First come the legionaries: a single dig, in 2021–22, turned up 123 stamped LEG XIII GEM tiles, and two bear people's names, Aurelius Enthimus and Flavius Martinus — craftsmen or suppliers, we do not know which. Then the cathedral masons, hired under the contracts of 1287 and 1291 kept in the chapter archive: their stone still holds the west portal.
Most stay nameless: the Romanian peasants brought to the Austrian building site, over 20,000 on the municipal pages' reckoning — a reported reckoning, not a proven one, since no ledger has been published. The 1849 garrison has no names on this page either: all we know is it held the walls for four months. And the 1918 delegates have their own page: Alba Iulia 1918.
St Michael cathedral choir and the Michael the Brave statue. Photo: NT87, CC BY-SA 3.0 RO, via Wikimedia Commons.
Layers: each fortress with its years
Three fortresses stand one over another on the same terrace, and each swallowed the older one. The table sets them in order, with what can be seen of each today.
The fortress layers and their years
Layer
Years
What can be seen
The Roman camp
c.106–275
principia, south gate, museum walls; measure disputed
The medieval fortress
12th–17th c.
St Michael's cathedral; walls on the Roman plan; two Bethlen works
The Vauban star
1715–1738
7 bastions; 6 gates + passage VII; ditches 25/15/12 m
The siege
1849
the walls that held; the Batthyaneum journal
The 20th century
1918–1922
Union Hall; Coronation Cathedral; 15 October 1922
Today
1991–2027
70 ha built; UNESCO waiting list; east ditch works
Eight statements: true or false?
Choose. The answers check out against the page's sentences.
The fortress star has seven bastions, not seven towers.
Alba Carolina fortress was never attacked.
The 20,000 labourers and 2 million gulden are reported reckonings, not proven ones.
Alba Carolina fortress is inscribed on the UNESCO list.
Gate VII is the seventh monumental gate, like the other six.
The great ditch is 25 metres wide, more than the others.
On 15 October 1922 Ferdinand set the crown on his own head.
It is known for certain which town was Colonia Nova Apulensis.
Liked it? Send the page to a history teacher.
How we worked and what we do not know
The fortress measures come from the Alba Iulia City Hall technical description, read in full: bastions, ravelins, tenailles, ditches, gates. The UNESCO map is waiting list 555, read in full. The 1849 siege comes from the Sargetia study abstract and the county page, since the full text sits behind an anti-robot wall. Where the sources disagree — the camp's measure, the 70 against 110 hectares, the finishing year — the page shows both variants and says which was drawn and which was built.
The 3D section is schematic: the star's angles are drawn, not surveyed off Visconti's plan, and the layers sit one over another more heavily than in the ground. What we do not know yet: how many people truly laboured on the site, what the fortress cost to the last gulden, and which town was Colonia Nova. When ledgers or new digs appear, the page changes.
