The head and helmet were modelled in Zbrush subdividing to 4.5m polygons for detailing and polypainting. Finally I created UVs, texture maps and normal maps (all within Zbrush) so that I could export the relatively low-poly version seen here as an FBX file.
I am working on a full figure of a Roman Centurian and plan to publish a posed and a T-posed version.
My thanks to Samize for his excellent model of a Roman helmet which I used for reference https://skfb.ly/6RYLu