A milliarium (Roman Milestone),

Barca da Mó, near Caldas do Gerês, Portugal. This Hadrianic milestone is one of several in place along the Roman military road to Bracara Augusta (modern Braga). © 1993 Craig R. Bina [Images] [Archaeology]

Link: http://www.earth.nwu.edu/people/craig/archaeology/figs/miles.gif