Age of Empires II: Definitive Edition (PC) - Achievement - A Truly Holy Emperor

Age of Empires II: Definitive Edition (PC) - Achievement - A Truly Holy Emperor

Convert the Cathedral in Milan without acquiring a single Villager in the third Barbarossa mission "Pope and Antipope".

This method involves a little sneaking, but isn't all that difficult. Start by sending your priests on the transport as close to the Cathedral as possible and then disembark. Send the transport back and try and bring the rest of your units if there's time, but if not, take your strongest as the 5th initial member on the boat.
As long as you don't attack or go to close to their military, they will not attack you. The first thing you need to do is get inside the city. Keep your troops close to the gates and wait for an opportunity. There is a relic just outside of the enemy base that they will send a priest to collect. There are also sheep you can take which can help. Purposely lose the sheep to the enemy and try and follow it in as they bring the sheep within their walls. They also occasionally send trade carts through the gates. Careful not to block the gates too much or it can stop the enemy using them as it will detect the path is blocked. If all this fails, units will occasionally use the gate and you should eventually be able to get in. The more troops you get in the better, but try and get all your priests in. Any other units are a bonus that will help defend to buy your priests time while they convert the cathedral. Careful to avoid enemy units - there is a mangonel fairly close to the route in the video as well as an enemy priest near the cathedral itself. Troops will be quick to react once you start converting. Just buy time and protect your priests.

UPDATE: The December 17th 2019 update has fixed many issues relating to achievements. This should no longer be bugged.

https://www.youtube.com/watch?v=emIuVqL2U2A&feature=youtu.be

Age of Empires II: Definitive Edition (PC) - Achievement - A Truly Holy Emperor

Age of Empires II: Definitive Edition (PC) - Achievement - A Truly Holy Emperor

Convert the Cathedral in Milan without acquiring a single Villager in the third Barbarossa mission "Pope and Antipope".

This method involves a little sneaking, but isn't all that difficult. Start by sending your priests on the transport as close to the Cathedral as possible and then disembark. Send the transport back and try and bring the rest of your units if there's time, but if not, take your strongest as the 5th initial member on the boat.
As long as you don't attack or go to close to their military, they will not attack you. The first thing you need to do is get inside the city. Keep your troops close to the gates and wait for an opportunity. There is a relic just outside of the enemy base that they will send a priest to collect. There are also sheep you can take which can help. Purposely lose the sheep to the enemy and try and follow it in as they bring the sheep within their walls. They also occasionally send trade carts through the gates. Careful not to block the gates too much or it can stop the enemy using them as it will detect the path is blocked. If all this fails, units will occasionally use the gate and you should eventually be able to get in. The more troops you get in the better, but try and get all your priests in. Any other units are a bonus that will help defend to buy your priests time while they convert the cathedral. Careful to avoid enemy units - there is a mangonel fairly close to the route in the video as well as an enemy priest near the cathedral itself. Troops will be quick to react once you start converting. Just buy time and protect your priests.

UPDATE: The December 17th 2019 update has fixed many issues relating to achievements. This should no longer be bugged.

[Scholar-at-Arms]

Video guide was on normal mode. For hard mode, you additionally need to research Redemption, which requires selling resources until you can afford it. Additionally, enemies will aggro onto you as soon as you enter sight radius, so bring everything.

[bronze_aged]

I couldn't get through the gate BUT as Sokar said, you can sneak around the south through the trees. Then I followed the instructions from there, using units to distract while the monks converted. The enemy cav couldn't kill them quick enough. Thank you!!

[BinkyBoyZ]

The only way I could get enough time to convert is by attacking the monks and cavalry for just a second before starting the conversion. If you convert before attacking anything, all units will head straight to your monks. So, if you attack them for just a moment first before starting the conversion, they won't have enough cavalry to take your monks down in time, and their priests will be dead so they can't convert your monks.

[BinkyBoyZ]

The video provided a good starting point for me. Unfortunately, unlike the video, I couldn't reliably get the River Guard throwing axeman to open the gate, the Milan monk would come out for the relic way too late, and there were no trade carts. I used a knight to attack the Milan wall near where the river ends to get the mangonels to attack it, and I then moved the knight away from the wall just enough to keep aggro and force them to head towards and out of the gate to allow my other units to enter. One way to get your units as close as possible to the Milan gate without attacking it is to use attack move.

For the cathedral I used 4 monks, 3 pikeman, a knight and a scout (2 trips total with the transport ship). After walking from the gate south and arriving at the cathedral, I distracted each of the 2 monks with my 2 horses, their cavalry with my pikeman.

[Sokar]

But I remember in CD version, there was a different way. There is a small gap in the cliffs at the very south of the map. But at the start, its blocked off by a tree. When I beat the mission "normally" (with units and stuff), I send a scout there and the tree was missing. I don't know if it was removed by a trigger or a random villager if milan cut it down for me, but it was definately missing. If it could be triggered earlier (or wait it out, but then milan probalby has too many units), that could a path. Or is it just a tease by the developers?

[Sokar]

Sneaking Units in is probably the intended way. I did it this way (on Standard Difficulty)
1. Ferry all units over
2. Group: 1 Knights and Scout, 2 Pikemen, 3 Monks (or whatever grouping suits you)
3. put all Units on not attack stance
4. try to move inside the gates. Your units will line up before a gate
5. wait until it opens. For me, a friendly Axe-Thrower of the river guard did it.
6. move all units to the cathedral
7. reset unit to attack stance
8. Use Scout and Knights to kill the monks near the cathedral, they already should be in sight
9. move the pikemen south of it, to catch the light cavalry stationed their
10. use the monks to convert. The left or bottom side seem ok, but gets tricky if the mangonels move up there.
11. micro units to keep the monks alive by keeping the enemy units off them

[Lord Necronomus]

Eres un capo

[BloodshotHippy]

Must have been lucky because there were at least 20 units down there at the cathedral for me. Including range that killed all my monks within a matter of seconds.

[Alex]

I actually did this on hard recently - You just have to get one of your units to attack away from the cathedral when you're inside the walls and all of their units will go rushing towards it allowing you to make a break for the cathedral with your priests. There are two relics as well to pick up if playing on hard, because you don't even start with the technology to convert buildings haha so you need to quickly get them and deposit them to get the gold to research.

[Lukster Lee]

Never mind, I tried again on the easiest difficulty and it is indeed possible to obtain this achievement exactly as shown in the video.

Bumping up the difficulty to Moderate is when it became impossible. Milan receives far more starting units all around Cathedral the higher the difficulty and they respond with everything they have as soon as you approach the Cathedral, including more Monks.

Big Thumbs up for your guide.