Age of Empires II: Definitive Edition (PC) - Achievement - Church Sanctuary
Do not lose any Tarsos Villagers in "Of Turncoats and Traitors".
This achievement triggers, if done successfully, after the initial 'siege phase'.
You start with 20 Villagers and cannot train more. These 20 Villagers must survive the siege phase (until the counter gets to 0:00).
Armenians can build Fortified Churches to garrison troops in which do attack, however the enemy occasionally attacks with Rams and Trebuchets, so you would run the rusk of a church with Villagers in it being destroyed outside the walls if you choose to do this.
Be very protective of your Villagers when they are outside the walls - If one dies, the achievement will not trigger. You lose control of this base after the siege phase, so don't worry about sacrificing walls / buildings to protect your Villagers. You can garrison them all in the Castle towards the end to be safe. You just need to make sure you've used them to gather enough resources to survive the initial phase, then just focus on keeping them alive.
Some people have mentioned the achievement not triggering if any / all settlers are garrisoned when the timer gets to 0:00, so it would be best to ungarrison them to be safe, just prior to the timer reaching 0:00.