Hi BtSH Players

I would like to join. I already read the rules, which I know partly from WotB.

But I have a question. I read:

"All Players enter the game at the rank of Legatus. "

But there is another Rank, Tribunus, who is the third in command and has to serve UNDER a Legatus. So who is Tribunus. Don't players start as Tribunii?

Greetings SB