Segni has an ancient and fascinating history. The majestic system of polygonal walls (dating back to the fifth and fourth century. A. D.) and the vast architectural complex of the Acropolis tell of the ancient origins and of the development in the Roman era of the city; the cathedral and the urban structure of the historic centre (with its charming rectangle of streets and its rich, noble palaces) show the intense building activity of the middle agesand the rebirth of the city after its sacking in 1557 at the hands of the French.
The frequent Papal visits to the palace that would then become the Episcopal Seminary would create even more prestige and notoriety for the city between the twelfth and fourteenth century.

Between the end of the sixth century and the beginning of the next one Pope Vitalianus was born here and was later to become a Saint, he ruled as Pope from 657 to 672 AD

In the town Library a digitalized copy of the Segnini statutes from the renaissance era and post-renaissance era (kept in Rome at the Senate Library) testify to the sophisticated institutional life of the community, in the course of history, while the numerous accounting documents detail the importance of chestnuts as a resource for the local economy even from the Middle Ages, and they reconstruct the recent diffusion in the last century through grafting, of the magnificent chestnut of Segni.

The city has paid its dues in blood during the Second World War in the course of two tragic bombardments between the autumn of 1943 and the spring of 1944, losing tens of human lives and the edifice of the Church of Santa Lucia.