Age of Empires II: Definitive Edition (PC) - Achievement - Italy Jones and the First Crusade
Do not lose a hero in the fourth Hautevilles mission "Bohemond in the East".
This mission can be a little overwhelming to begin with. You start with a large walled city that is soon besieged by several waves of invaders. You begin with hero units scattered around your perimeter. To be safe, I immediately gathered them and moved them to the centre of the city and ordered them to stand ground. This takes them out of the equation completely unless you you allow the enemy to reach that for into your city.
There is an optional mission to destroy Ahmed iba Marwans (Green) garrison. If you choose to do this, it allows you to explore a little south-east revealing small amounts of gold and stone. Alternatively, you can use your market to obtain the resources you need.
Just survive the waves or make a charge to Kerbogha and kill him to complete the mission. Garrisoned Donjons are quite useful in defending your city with.