Create a new scenario.
Build a wall around 30-40 priests on your team to create a pit.
Place 25-30 club men from the other team (team 2) into the pit.
Change your starting age to Post-Imperial.
Change your civilisation to Egypt.
Save your scenario and load it up through Single Player > Custom games.
Sit back and enjoy your achievement.
If it doesn't unlock, just replay the mission again as too many club men may have been killed by converted ones or too many priests died.
This achievement is cumulative over multiple maps.