Alatri Geography, Climate & Nature

Alatri rises on a twin hill of the Latin Valley, on the slopes of the Monti Ernici, which form the natural boundary of Lazio with Abruzzo.

The comune spans a substantial vertical range. Intermediate elevations between 300 and 600 metres predominate, accounting for nearly half the territory, while a not inconsiderable part rises above 1,000 metres. Overall the land falls from the southern spurs of the Ernici to a minimum of 175 metres on the plain of Tecchiena. Among the peaks are Monte Brecciaro and Monte Cappello.

Water organises the lower ground: the territory takes in much of the basin of the river Cosa, a tributary of the Sacco, which flows east of the town centre on a predominantly north–south line.

The geology explains the walls. The territory is composed largely of white-yellowish granular limestones with the large rudists characteristic of the Senonian — and it is that well-bedded local limestone the megalithic circuit is built from. The lower areas, such as the valley of the Cavariccio torrent, are instead volcanic tuffs: pozzolana and peperino.

Alatri's climate has transitional characteristics, between the inland hill environment of Lazio and the Mediterranean pattern of central Italy.

Summers are short, hot, dry and mostly clear; winters are longer, very cold and partly cloudy, with a marked alternation across the year between a stable sunny summer phase and a damper, more variable autumn–winter one.

In temperature terms the year generally runs between about 0 °C and 30 °C, with values below −4 °C or above 34 °C rare. The hot season lasts from mid-June to mid-September, with August the hottest month at an average maximum of 29.2 °C. The cold season extends from mid-November to mid-March, and January is the coldest month.

The wetter phase runs about seven and a half months, from mid-September onwards.

The comune's own altitude range reinforces all of this: nearly half its territory lies between 300 and 600 metres, and a significant part rises above 1,000.

Alatri's territory runs from a valley plain up into the Apennines, and the geology changes with it.

The upper ground is the Monti Ernici, which form the natural boundary between Lazio and Abruzzo, with a not inconsiderable part of the comune rising above 1,000 metres and peaks including Monte Brecciaro and Monte Cappello.

Most of the territory sits in between: intermediate elevations of 300 to 600 metres account for nearly half of it, falling to a minimum of 175 metres on the plain of Tecchiena.

The water system is the river Cosa, a tributary of the Sacco, whose basin covers much of the comune and which flows east of the town on a north–south line.

The geology is split in a way that shows in the vegetation: largely Senonian granular limestone across the higher ground, with volcanic tuffs — pozzolana and peperino — in the lower areas such as the Cavariccio valley, where a fracture runs visibly through the terrain parallel to the torrent.

The wildlife here belongs to the Monti Ernici and the Latin Valley beneath them.

The Ernici are the significant habitat. They form the natural boundary of Lazio with Abruzzo, and the part of Alatri's territory rising above 1,000 metres connects to that range rather than ending at the town — which links it, over the border, to the larger Apennine systems of Abruzzo.

The limestone is the defining substrate up there, and limestone uplands carry a distinct flora from the volcanic country that dominates much of western Lazio.

Lower down, the Cosa basin is the water corridor through farmed valley ground, and the Cavariccio valley with its volcanic tuffs is a different soil environment again.

The constraint is the Latin Valley itself: a long-settled, long-farmed corridor between Rome and the south, with the fragmentation that implies.