near Brosso); between Strambinello and Baldissero Canavese the continuity of the hill chain is then interrupted by the gorge by which the Chiusella veers eastward heading toward the confluence with the Dora Baltea.

[5] The frontal moraine, on the other hand, consists of a succession of hills that extend between Agliè and Viverone and are interrupted between Mazzè and Villareggia by the gap opened by the Dora Baltea.

[5] Within the amphitheater lies the vast flat area, whose elevation is generally between 210 and 270 m above sea level, in which numerous population centers, including the city of Ivrea, are located.

[5] The continuity of this plain is interrupted here and there by isolated reliefs and a few minor hilly cordons; one of these defines within it the Small Morainic Amphitheater, centered on the towns of Strambino and Scarmagno.

[10] Traces of this legend may also be found in the chronicle De bello canepiciano, compiled by Pietro Azario in the 14th century, in which the ancient presence of a large lake in the area is reported as certain news.

[14] According to geologists, in the final phase of the Pliocene, the geological period that preceded the formation of the morainic amphitheater, in the Canavese area the sea that occupied the Po River basin at that time and reached into the interior of the Aosta and Orco valleys was gradually filled in by sediments originating from the erosion of the Alpine range.

[14] The AMI, on the other hand, formed during the Pleistocene when, due to decreasing average temperatures and increased precipitation over the Alpine arc, a considerable mass of ice began to accumulate and was carried downstream by large glaciers.

Later this classification was no longer considered sufficiently accurate to describe the geological evolution of the basins located south of the Alpine chain,[4] so that the current subdivision of the moraine circles became the one shown in the following table (reworked from the Geological Map of the Serra Morainic Amphitheater):[14] The deposits left by the oldest of the three main glacial pulsations (San Michele - Borgo group) are the outermost and are best identified on the left side of the AMI, in the Biella area of the Serra.

The hilly reliefs due to this glacial phase are the ones that reach the greatest heights partly because they were to some extent curbed by the presence of the moraines left by the previous pulsation, which resulted in a higher elevation than would have occurred in the case of undisturbed deposition on a flat area.

The third group of deposits, referred to as the Bollengo-Strambino (or also Bollengo-Albiano), is the most recent and is located within the previous two; it includes some moraine cordons of lesser elevation development as well as the Serretta, a low hill that breaks away from the main body of the Serra near Bollengo.

[14] The other glacial episodes that have marked Pleistocene history left no traces in the area because their deposits were later covered and/or displaced by the sedimentary masses related to the three main morainic circles.

[4] The creation of the large morainic apparatuses at the outlet of the Aosta Valley not only had an impact on the area now included in the AMI but also substantially modified the hydrography of the neighboring territories.

Paleogeographical research (in particular by geologists Francesco Carraro[15] and Franco Gianotti[16]) shows, for example, that in ancient times the Cervo stream, after leaving the alpine valley of the same name, headed decisively southward and flowed into the Dora Baltea roughly where Verrone stands today.

However, the deposition of the enormous morainic apparatus of the Serra and of sedimentary beds east of it changed this configuration and progressively diverted the course of the Cervo eastward, eventually leading it to flow into the Sesia.

while those to the east of the town, outside the AMI, have an average elevation around 260 m.[5] This phenomenon is due to the erosive action of the Balteo Glacier, the flow of which, during periods of maximum expansion, lowered the ground level, transferring part of the sediments that made it up into the moraine reliefs being formed.

With the progressive silting up of the lacustrine areas left by the retreat of the glacier, the Dora Baltea began to erode the sedimentary cover that constitutes the plains inside the AMI.

[note 3] With the final phase of the last glaciation, the areas that were being cleared of ice, albeit discontinuously and gradually, were occupied by vegetation that was initially herbaceous and shrubby and then forested.

[note 4] The retreat of the Balteo glacier within the present-day Aosta Valley is generally located around 20,000 years before the present;[20] at this early stage paleobotanical data indicate that the outer bands of the moraine amphitheater were occupied by thickets in which green alder and willows predominated while a continuous forest cover of larch trees had developed around Lake Viverone.

Today's satellite photographs of the area show, for example, how to this day the moraine hills still differ in the presence of extensive forests from the inland plain and surrounding territories, which are instead characterized by a denser human population and the prevalence of intensive farming.

There are, however, numerous human testimonies in the area dating back to the Neolithic period and, particularly, to the final phase of the last glacial pulsation of the Early Pleistocene (starting about ten to twelve thousand years ago).

[22][23][24] The human population was consolidated during the Bronze Age; among the finds dating back to this period particularly well preserved are those referable to settlements near lake basins that still exist or that over time have been transformed into peat bogs.

There were no noteworthy battles over the next forty years, but certainly Rome's economic penetration continued, which allowed the Senate to found the Roman colony of Eporedia (today's Ivrea[29]) in 100 BC on a pre-existing fortified village of the Salassians.

[31] This land organization of the lowland area took place according to the classic scheme of centuriation, that is, the division of fields with a network of orthogonal lanes and canals; traces of this ancient subdivision can still be found in the Canavese countryside, according to archaeological studies.

[33] As in ancient times, this part of the Canavese in the Middle Ages was traversed by an important communication route: the Via Francigena, which gave pilgrims from central and northern Europe a way to reach the city of Rome.

[28] Somewhat linked to the presence of the Via Francigena is the flowering of Romanesque architecture, which alongside religious buildings of considerable importance dotted the moraine hills with minor churches and chapels, often located in isolated places.

The tops of the hills that make up the AMI were in many cases used for the construction of castles and villages, which benefited in this way from more easily defensible and healthier positions because they were far from the flat areas that tended to be marshy.

[35] In the final phase of the medieval period, thanks in part to the relative political stability provided by the Savoy state, the area experienced a fair amount of economic growth; among the various works built in this period is the Naviglio di Ivrea, the construction of which as a navigable canal was initiated by Amadeus VIII based on a design by Leonardo da Vinci with the aim of connecting the city of Ivrea to Vercelli and irrigating the Vercelli countryside.

[39] Also in the post-World War II period, the AMI was affected by widespread building growth, especially in the area of the inland plain,[40] and the construction of various infrastructures including the Turin-Aosta highway and the A4/A5 - Ivrea-Santhià branch, or the so-called Bretella.