Discover Acropolis of Alatri

Alatri, Latin Aletrium, is a town in the province of Frosinone, and what it is known for is its megalithic acropolis -- a circuit of enormous unmortared blocks crowning the hill at the centre of the town. It was an ancient city of the Hernici, and the area was already settled in the second millennium BC.

The acropolis of Alatri is a masonry argument. Several courses of polymorphic megaliths, cut from the hill they stand on, are fitted perfectly into one another without lime or cement -- the technique called opera poligonale, where each block is worked until it matches its neighbours rather than being squared to a module. Flat ground was made at the top partly by smoothing the rock off and partly by raising terrace walls that rise over 15 metres.

It is not one campaign, and that is the key to the dating. Remains of fortification from three successive periods can be traced here. In the first two the construction is rough; in the third -- the best preserved, and probably a little later than the city wall below -- the blocks are very well jointed, their faces smoothed, mostly polygonal and much larger than those of the town circuit, reaching about 3 by 2 metres. Sources differ on the enclosure those walls make: the Italian account describes a trapezoidal area of 19,000 square metres, the English a roughly rectangular one of 220 by 100 metres.

The question the walls raise is whether their shape means anything. An archaeoastronomical reading proposes that the perimeter retraces the figure drawn in the sky by the constellation Gemini at the summer solstice. The more probable explanation, as the source itself says, is that the particular outline is an adaptation to the natural shape of the hill. A similar question hangs over the two gates, whose height-to-base ratio approximates the golden section.

What is not in doubt is the engineering of the openings. The Porta Maggiore spans its doorway with one enormous stone and runs back into an 11-metre dolmen gallery; the Porta Minore covers its corridor by corbelling nine monoliths progressively inward, a roofing method whose only parallel is inside the pyramid at Egyptian Memphis. Two completely different solutions to spanning a gap, in the same wall. The architrave's dimensions are themselves disputed -- 4.0 by 5.13 by 1.3 metres and an estimated 27 tonnes in one account, about 5 metres long by 1.5 high and 1.8 thick in another, which agree on the length and on little else.

The stone came from under their feet. The megaliths are polymorphic and were quarried from the same hill the acropolis stands on, then worked until they interlocked without mortar of any kind. Nothing had to be carried far, and nothing had to be squared to a standard. The summit was levelled partly by smoothing the rock and partly by terrace walls over 15 metres high.

It was built at least three times. Fortifications of three successive periods can be traced on the hill. The first two are rough work; the third is the best preserved and probably slightly later than the town wall below, with blocks up to about 3 by 2 metres, very well jointed and their faces smoothed. A visitor looking for one uniform wall is looking at a sequence.

When all this happened is genuinely unresolved. The French archaeologist Louis Charles François Petit-Radel placed the foundation of Alatri before the Second Pelasgian Colony of 1539 BC. Archaeological scholarship has argued instead for a Hernican origin with a general restructuring in the Roman period. Some researchers put the walls in the sixth century BC and others fully four centuries earlier; Filippo Coarelli has proposed the fourth to third century BC. No reading has displaced the others.

A Roman censor left his receipt. Lucius Betilienus Varus recorded the public works he had built in an epigraph, and two of them are still traceable: a lacus ad portam, which the cistern found beside the Porta Maggiore during recent work on the via Gregoriana -- and since reburied -- is thought to be, and a high-pressure aqueduct that supplied the town. He also built the colonnade from the forum up to the acropolis ramp, in the second half of the second century BC.

The medieval town on top was demolished by order. In the Middle Ages the acropolis lost much of its sacred function, was fortified and absorbed into the inhabited centre, with numerous houses built inside it; ruins of that settlement have been found. It was destroyed in 1326 on the order of the rector of Campagna e Marittima, following the expulsion of Francesco de Ceccano, who had installed himself and occupied it. From then only the cathedral of San Paolo and the bishop's palace remained, the latter rebuilt between 1337 and 1342 with a prison in its cellars. A building had stood at the centre of the arx on the site of the present cathedral, and only a small part of it is preserved.

The town cleaned it up for a pope in ten days. The acropolis was restored in 1843: for the visit of Gregory XVI the citizens of Alatri worked ten consecutive days to clear the walls and build an access to the upper part of the ancient city, making the road that runs round the perimeter -- named the via Gregoriana in the pope's honour. Ferdinand Gregorovius, visiting a few years later, wrote that standing before the construction he felt a greater admiration for human strength than the sight of the Colosseum had inspired in him. The stairway up to the Porta Maggiore is part of the same nineteenth-century work.

The twentieth century planted it and plumbed it. Long rows of trees were set across the surrounding esplanade, turning the acropolis into a park in the heart of the town, and a stone building was raised against the cathedral to conceal a water tank.

How old are the walls?

Unresolved, and the range is enormous. Petit-Radel placed the foundation of Alatri before 1539 BC; archaeological scholarship has argued a Hernican origin with Roman restructuring; some put the walls in the sixth century BC, others four centuries earlier, and Filippo Coarelli has proposed the fourth to third century BC. Part of why the spread is so wide is that there is no single wall: fortifications of three successive periods are traceable, the third the best preserved.

How big is the architrave of the Porta Maggiore?

Accounts differ. One gives 4.0 by 5.13 by 1.3 metres with an estimated weight of 27 tonnes, second in Europe only to the Lion Gate at Mycenae; another gives about 5 metres long, 1.5 high and 1.8 thick. They agree on the length.

How large is the enclosure?

Also disputed: a trapezoidal area of 19,000 square metres in one account, a roughly rectangular 220 by 100 metres in another. The terrace walls that make the flat summit rise over 15 metres.

Do the walls really trace a constellation?

It has been proposed that the perimeter retraces the figure drawn in the sky by Gemini at the summer solstice. The source notes that the outline is more probably an adaptation to the natural shape of the hill.

Why is it called the Porta dei Falli?

For the three phalli carved in relief above the door, now weathered, symbolising fertility. The gate is also called the Porta Minore and the Grotta del Seminario, and the passage is thought to have served pagan rites.

What is on the acropolis now?

The co-cathedral of San Paolo and the bishop's palace, rebuilt between 1337 and 1342. A medieval settlement stood up here until it was destroyed in 1326 by order of the rector of Campagna e Marittima. Since the twentieth century the esplanade has been planted with trees.

What is the via Gregoriana?

The road running round the perimeter, built in 1843 when the citizens of Alatri worked ten consecutive days to clear the walls and make an access to the upper town for the visit of Pope Gregory XVI, and named in his honour.

Which way up is easiest?

The ramp on the north side. It was added later than the gates, though probably still in antiquity, and it is where the colonnade Betilienus Varus built from the forum ended. A limestone lion stands at the top of it.