Age of Empires II: Definitive Edition

It's an easy achievement, first, build a couple of towers to the west of the wall and some palisades along the coast; this will delay the invaders, most of them will attack those points. Now, in your wonder, start recruiting Saxons and kill them as soon as they are recruited.

The Saxons will start building barracks near your southeast; you can build palisades over these to block their units. Now, the most important thing is to focus on your economy; in your camp to the southwest, you can focus on wood, and you have a camp to collect stone for your towers, try to focus on food. Remember to kill green enemy units that are nearby.

Try to advance to the Castle Age quickly and start producing units from the barracks and knights. Place them in the Saxon camp; you can also use some catapults to damage Saxon buildings. When the Saxons betray you, you'll defeat them quickly; make sure you have recruited them at least 12 times.

Surviving to the end of the game is simple, and you shouldn't have any major problems; the wall will easily withstand it.

Also you can get Civis Romanus with this method.