How Alatri was built and evolved over time

The acropolis walls are the only piece of construction most people come to Alatri for, and they repay close attention.

They are polygonal fortifications, constructed from well-jointed local limestone — irregular blocks cut to fit one another precisely without mortar, which is what "polygonal" means in practice and why the masonry reads as a puzzle rather than a course.

Structurally, the circuit is almost entirely an embanking wall, as is the rule in the cities of this part of Italy. That is a significant distinction: it is retaining the hill rather than standing free as a curtain, which is why it has survived where free-standing walls did not.

Its scale is specific: a maximum height of probably about nine metres.

And the openings are where the work is legible. Two of the gates, out of perhaps five that once existed, are still to some extent preserved, and three posterns can be found.

The material came from directly underneath. The territory is composed largely of white-yellowish granular limestones with the large rudists characteristic of the Senonian — the stone of the walls is the stone of the hill.