Fortify the mesa and survive the enemy attacks until time runs out.
Town Center Must Survive
Quest Giver Dialog
“ It would seem I must again stoop low and allow you to assist me.
You can, of course, thank me for this honor at any time.
As for the next task, we must begin construction on the nearby mesa. You will be outnumbered by the Nubian tribes in the area, so do all of that military stuff that prevents the enemy from getting through, and try not to fail. ”