Nestled in a valley flanked by morainal hills, Longone al Segrino retains fascinating traces of local pre-history and Roman times.

In 1894, during the construction of the Bramani villa, near the lake, three Celtic tombs made from rough slabs of gneiss were discovered. The three tombs contained blackish, smoothed, decorated terracotta vases. They also held several bronze jewels (rings, bracelets, earrings, necklaces, clasps, buckles). Earlier still, in 1765, a marble altar dating back to Roman times was found during an excavation of the foundations of the oratory of Santa Maria. In 1880, more Roman tombs containing, among other things, coins from the eras of Diocletian and Constantine the Great were discovered.

The most significant find, however, would come in 1866: five Roman tombs in what was then Tagliasacchi Park. Three of them were built with gneiss slabs, the other two in masonry. They contained human skeletons, items made of glass, terracotta and metal and some Roman coins. Lastly, in 1910, a sepulchre hollowed out of a block of serpentine was found in a meadow in Beldosso. It is known that Longone became part of the Roman Empire in 222 BCE when Caecilius Metellus was proconsul.

Since the settlement was close to a lake fed by underground springs, the Romans were keen to ensure its protection, and did so by dedicating it to the gods. They called it Fons sacer: the sacred fountain. Over time the name transitioned to Sacrino, later becoming Segrino.