Alatri is one of the several towns of ancient Latium Vetus with outstanding Cyclopedean (Megalithic) walls – that are referred to geometrically as Polygonal Walls.
These walls surround the acropolis of Alatri and the acropolis may tell us the story of gigantic stones in these walls. The term Cyclopedean comes from the gods, from reference to Saturn who the ancient Romans thought must have been the founder of these towns as it would have been difficult to conceive how any earthly man could have built these walls with the enormous stones, stones that fit into each other perfectly, without mortar.
Maybe man (or some Brobdingnags) were involved, yet we know little about these pre-Roman engineering skills that seem to have been abandoned after the creation of these walled towns.
The stones are enormous, up to at least 5 metres by 2 metres by 1,5 metres, a stone that weighs maybe 25 tonnes, not all that easy to move into its idealised position as the lintel above the Minor Gate on the western side of the acropolis of Alatri (an acropolis that shares with that of Athens the distinction of not having been hidden by rampant construction).
But why polygonal? Why do blocks of all these walls interface with each other with 9 or more corners, why does each wall rise and fall irregularly with blocks all of different sizes and shapes? Let us gain an insight from the ‘Portal to the History of Astronomy’ discussing the acropolis of Alatri: ‘A continual problem for the dry, polygonal masonry is the growth of tree roots inside the earthwork that stands behind the walls. ….. Unfortunately, an attempt at restoration was made in the 1970s, in which cement was injected in some sectors; this has caused a series of problems because the masonry cannot oscillate and the area is one of high seismic activity. However, it seems to be impossible to restore the pre-restoration situation, so the monument is (for the first time in millennia) at some risk from earthquakes.’
So, putting aside the construction challenges faced by the ancients with these Megalithic stones and the Polygonal walls in these Latium Vetus towns, walls that have lasted for well over 2.500 years, maybe we can look at the mechanical design and toss the coin on possible reasons for the design.
Maybe the key is in the reminder that ’the area is one of high seismic activity’. As we have witnessed to our mortal dismay there has been in central Italy over the last ten years, the destruction of several towns and villages of medieval, renaissance and modern architecture on the occasion of serious earthquakes.
Is it possible that the ancients knew enough physics to design and construct quite high structures that could withstand such earthquakes?
There are four obvious design features of the Cyclopedean walls that could contribute to the resistance to earthquakes. The first is the size of the blocks – all large and not readily able to be brought into resonance by a tremor.
The second is the blocks are all different size and shapes so that if one block were to resonate with a tremor, other blocks may not. The third element is the selection of the rocks that all seem to have non-critical defects that can stop or reduce the transmission of a defect caused by a major shock. The fourth is imperfect interconnectivity between the blocks – the interfaces are a combination of points of connectivity of the rocks and ‘air’.
There is no mortar to create a continuous mechanical element that would transmit a shock wave. The experiment of restoring the walls with cement (mortar) has brought home the realisation that there was great skill in the hands of the pre-Roman engineers.
The grand purpose for this marvelous engineering may not be understood but it is now apparent that the designers knew how to build for ‘eternity’!
A report from the studies by Don Giuseppe Capone (translated into English by Anthony Aveni), provides some guidance about each of these acropoli – which were all of irregular geometry. ‘There may be contained in the Alatri map the identity of an ancient people, who came from a far shore and here re-established their culture with this majestic city in stone’. But why did they come?
In any case, next to a Cyclopean wall of the acropolis of Alatri may be a relatively safe place to be in the event of an earthquake.