The colonel commanding the MEU would have to combine cunning with a level of ruthlessness not seen in Western warfare since the SS were defeated. He would also have to be able to manipulate Roman religion, supersticions, etc. You are after all an alien society that has a greater understanding of your target than they have of you. That is your chief advantage.
“He would also have to be able to manipulate Roman religion, supersticions, etc.”
Don’t forget folks. The MEU’s officers will include ACADEMY-TRAINED people, who would be fairly familiar with this period’s history, it’s politics, and ROTC Officers with very specific skill-sets, and technical engineering.
They would know what is possible, and be able to adapt local materials in to say, steam engines, over the long term.
Gunpowder would be easily made from local resources.
And the 15 day internal load of an MEU would translate in to MONTHS, or even years, against such a low-tech adversary.