It should be noted that the names for these helmets are not Roman in origin. Archaeologists named them based on their appearance or where they were first unearthed. In his 1975 book, The Armour of Imperial Rome, H. Russell-Robinson formulated a typology for Roman helmets, which is the standard for helmet discussions to this day. This book is out of print and difficult to find. Fortunately, a synopsis is available on RomanArmy.com

I illustrate a few of Robinson’s types bellow.

	Montefortino Helmet 4th century BC to the 50s AD. The Romans copied this style of helmet from the Gauls and Celt-Iberians. The legions of Julius Caesar’s time would hvae worn helmets like this. There is an attachmen at the top for a horsehair or feather plume. It is named for the find site, the Necropolis at Montefortino, in northern Italy.
	Coolus C Late Augustan to Tiberian period. This type of helmet was very well made. The horizontal ridge along the brow was put in place to prevent sword blows from hitting the main headpiece. It is named afrer the Coolus region of the Marne River valley in present day France where examples were found.
	Coolus E Late Augustan to Tiberian period. Unlike the Coolus C, this helmet was mounted with side tubes for plumes and a top spike for holding a horse hair crest. This crest would be held in a small metal box, rather than the Republican era method of gathering all the hair at one point like a paintbrush. As more advanced forms of helmet were developed the Coolus was continued to be used by auxiliaries.
	Imperial Gallic H 1st century AD. The embossed eyebrow pattern at the front of the shull cap displays a Gallic influence, resulting in the name of this family of helmets. The drawing shows a Gallic H, which featured a more sloping neck gaurd then found in previous Gallic types.
	Imperial Italic G 3rd century AD. The term "Italic" applies to a whole family of Roman helmets all sharing a similar style. They were used at the same time as the Gallic types. A notable difference is the fact that the Gallic embossed eyebrows are missing.
	Spangenhelm 3rd century AD. (this term, Spangenhelm, is best applied to helmets from the Middle Ages.) Believed to have originally been developed by the Sarmatians, this helmet was relatively easy to produce. It was made of between four and six curved iron plates shaped into a bowl and riveted together by bands or Spangen. Adopted by the Romans in the 3rd century AD, it continued to be used by European armies well into the 7th century.
	Roman Ridge Helm 4th century AD. This helmet appeared with the end of the production of the Gallic style helmets. It consisted of two curved plates connected by a central ridge. To this cheek pieces, neck guard, and sometimes nose piece were added. They were manufactured in huge quantities for infantry and cavalry. By this time the Empire found it more cost effective to reduce the armor of the legions. A helmet and a shield would, on most ocassions, be the only armor a Roman soldier would receive. The style may be from a persian influence.