Yasminou's description works mostly, but i'd like to add a few things..

Tank can pull both pack of mobs from the staircase by jumping down and climb the second staircase or provoke (20 yalm range works) one of the guards from the first staircase..
Tanks need to stun/stunlock if paladin the colossus to make them stay still on the cannon shooting ground, they always target random players on its enmity list with instant fire aoe which hurt the cannons..

Praetorium is mostly pretty straightforward,
Sac pull
Kill all
Sac pull
And pew pew all the baddies..