Roman helmets: Imperial Gallic/Italic and Ridge - comparisons and sources

[Marc Byrne]

The reason for change of equipment is not necesarily because the
new model is better/stronger, but because the type of warfare and the type of enemy is changing.
The Ridge helmet seems to offer more freedom of head movement and would be probably better suited for
the climate in Syrua and Messopotamia.
The Romans always adopted the armor and weapons of their enemies. Fashion is also an important factor.

Absolutely agree with this. The reasons for adoption of Ridge Helmets seems to me to be part of a number of complex and intertwined factors but tactical and fashion are two of the predominate one's.