Circello borders the following municipalities: Campolattaro, Castelpagano, Colle Sannita, Fragneto l'Abate, Morcone, Reino, Santa Croce del Sannio.

Snowstorms are quite common during winter (with snow sometimes present for 30 days or more), while the summers are mild with temperatures that rarely exceed 35 degrees Celsius.

Just a few kilometers from the center of Circello, there is an archaeological site at what was once the capital of Ligures Baebiani, a population of Ligurians who were deported from their homeland in 181 BC under the orders of the Roman consul Marcus Baebius Tamphilus, from whom (following Roman custom) they took the name Baebiani.

In 1831, the Tabula Alimentaria Ligurum Baebianorum was found in the Macchia district of Circello; it is an artifact dating from the year 101 AD, which lists the names of local landowners who had committed to investing in a fund for needy children that was established by the emperor Trajan.

The tablet was found in 1831 by Giosuè De Agostini at his own farm, and it was transcribed for the first time in 1845 by Raffaele Garrucci.