Also important were military chiefs, who had control over the frontier regions. They played both defensive and offensive roles, protecting the frontier and making cattle raids against neighboring tribes. Often, the Rwandan great chief was also the army chief. Lastly, the biru or "council of guardians" was also an important part of the administration. The Biru advised the Mwami on his duties where supernatural king-powers were involved. These honored people advised also on matters of court ritual. Taken together, all these posts from great chiefs, military chiefs and Biru members existed to serve the powers of the Mwami, and to reinforce the king's leadership in Rwanda.