I pride myself with being familiar with many of the early Christian heresies, but I have to admit this one was a new one for me.
The name "Circumcellions" somehow sounds like the name of an advanced Star Trek alien race, or perhaps a groundbreaking association of Ancient Roman jurists. The truth is so much less, and yet, at the same time, somehow, so much more...
The word itself means "guys who hang around villages," rather unglamorously. The Circumcellions were a Christian suicide cult of the fourth and fifth centuries. Their religious practice consisted of delivering random beatings to strangers along the road, with the purpose of goading the strangers into killing them. If that didn't work, they just threw themselves off a cliff instead.