The formula is a little bit provocative, but what other military helmet design have achieved such a long career?
Invented by the Celts in the 5th century B.C. it was adopted by the Romans (and other Italic populations) and with relatively small variants, it will be used until the first half of the first century of our era. Its adoption will be fairly rapid especially in Northern and Central Italy after the defeat against the Gaul’s of in the 4th century. With the new manipular Legion creation and the adoption of the Scutum and the pilum it will become increasingly popular. By the mid third century BC it will replace most other helmets as explained by Michael T. Burns from the Institute of Archaeology at the University College London in his excellent article: The Homogenisation of Military Equipment Under the Roman Republic.
During this period models are particularly well worked and worthy of the best Greek and Etruscans productions.
Starting in the second century BC its production will be gradually simplified as the soldiers stay longer and further away from Italy. It would be found more of what Russel.Robinson classifies as type B in the finding corresponding to this period. It is however most probable that a certain amount of surviving type A from the third century Bc were still in use.
At the end of the second century BC, with the Marian reforms this type of helmet will be mass produced. This will lead to a cheaper simplified model the type C. The shape is less round, the top button will be reduced to its simplest form, and the cord type decoration around the base of the helmet will completelly disapear.