In girum imus nocte et consumimur igni.
Sometimes you find it in a slight variation,
In girum imus nocte, ecce! et consumimur igni.
'Girus' is not a common Latin word; it's generally read as the Latinization of a Greek word, and if so it means 'circle' or 'ring'. Thus the translation would be, "Into the circle we go by night and are devoured by fire." The popular name perhaps arises from the sinister sound of it, but the saying is also often associated with moths circling a flame, which is what Augustus De Morgan explicitly had in mind when he applied to would-be circle-squarers in A Budget of Paradoxes:
The feeling which tempts persons to this problem is that which, in romance, made it impossible for a knight to pass a castle which belonged to a giant or an enchanter. I once gave a lecture on the subject: a gentleman who was introduced to it by what I said remarked, loud enough to be heard by all around, 'Only prove to me that it is impossible, and I will set about it this very evening.'
This rinderpest of geometry cannot be cured, when once it has seated itself in the system : all that can be done is to apply what the learned call prophylactics to those who are yet sound. When once the virus gets into the brain, the victim goes round the flame, like a moth, first one way and then the other, beginning again where he ended, and ending where he begun: thus verifying the old line
In girum imus nocte, ecce! et consumimur igni.
'Rinderpest' is also called cattle plague or steppe morain. It was a brutally nasty viral disease affecting the group of animals called 'even-toed ungulates', which includes cows, buffalos, giraffes, deer, and warthogs; in some populations fatality approached 100%. A vaccine was eventually developed in the twentieth century, well after De Morgan's comment. There are no known cases of rinderpest currently in the world, and have not been since 2001, due to a sustained half-century long eradication campaign; if this holds, it and smallpox are the only viral diseases that have ever been eradicated in the wild by human effort.
