Simplify the following text for a Grade 6 native English-speaking person.
Original: Within Great Britain , the territory which the Brigantes inhabited was bordered by that of four other Celtic tribes : the Carvetii ( to whom they may have been related ) in the North-West , the Parisii to the East and , to the South , the Corieltauvi and the Cornovii .
Simplified: The tribes that used to live next to the Brigantes were the Carvetti , the Parisii , the Cornovii , and the Corieltauvi .