The man in charge of the Roman Legions.
The role of Legatus was considered the highest rank that a legionary could strive to gain, while then it was still usually granted to a senator more often than a soldier who worked his way up through the ranks.
The Legatus was in charge of overall military strategy and campaigning. The Legatus would need to lean heavily on the other staff officers that would be surrounded by him, the business of day-to-day operations was run by these officers.
There were a few different “ranks” of Legatus in the Roman Army. There were Legatus in each province, in charge of their own regional legion, who would protect regional interests unless called upon by the Empire to go to battle, which was a common occurrence in the Roman times. (Milner)
One of the most important roles of the Legatus was to know when to press war upon his foes, and when it was time to hold back. In many cases the wisest Legate would listen to the senior “non-commissioned” soldiers who would almost always have the truest feel for what the soldiers were feeling and whether pushing the fight was wise. Vegetius was quoted, via translation, as saying that :
One should find out how soldiers are feeling before battle. Explore carefully how soldiers are feeling on the actual day they are going to fight. For confidence or fear may be discerned from their facial expression, language, gait and gestures. Do not be fully confident if it is the recruits who want battle, for was is sweet to the inexperienced. You will know to postpone it if the experienced warriors are afraid of fighting. An army gains courage and fighting spirits from advice and encouragement from their general, especially if they are given such an account of the coming battle as leads them to believe they will easily win a victory. (Keppie)
One of the largest dangers of the rank of Legatus is that they were subject to the displeasure of the Emperor. If a Legate has a bad campaign, they may not be long for the rank.
Keppie, Lawrence. The Making of the Roman Army: From republic ot empire. Lawrence: University of Oklahoma press, 1984. Print.
Milner, N.P. Vegetius: Epitome of Military Science. Liverpool: Liverpool University Press, 1993. Print.