Aracillum was a fortified Cantabrian city, scene of the third of the great battles of the Cantabrian wars (year 26 BC according to the chronology of E. Martino) between the Roman Empire and Cantabrian indigenous tribes. It would be located in the territory of present-day Cantabria, with two possible locations: , near Reinosa and the Roman city of Julióbriga; the second possible location would be the , in the . According to Roman historiography it belonged to the .