The Coolus helmet was a type of ancient Roman helmet. It was produced from brass and, like the Montefortino type with which it co-existed, was a descendent of Celtic helmet types. It was fairly plain, except for some ridges or raised panels on the cheekpieces. It was globular or hemispherical in shape (some were spun on a lathe rather than hammered to shape) with a turned or cast soldered- or riveted-on crest knob. The Coolus was replaced by the Imperial helmet type, a more developed form also derived from a Celtic original.