Age of Empires II: Definitive Edition (PC) - Achievement - Rome Was Destroyed in One Day
Destroy all Roman Castles before 30 minutes have elapsed in the fourth Alaric mission "The Giant Falls"
This is arguably the hardest campaign achievement in Age of Empires II: Definitive Edition. There are 12 Roman Castles to destroy in 30 minutes. Unless you are really good and highly experienced at this game, it will likely take multiple attempts. As such, before even attempting it, I would recommend starting the level and resigning immediately to reveal the map, so that you can get a gist of where everything is and the plan of attack we'll be using. On the positive side, you will have two allies in this mission who actually contribute towards taking out the castles, but not to the extent where they will do everything for you - far from it.
The game plan - There are a few castles which can be sniped by Trebuchets from outside the Roman Walls which I would highly recommend doing. I do this to two of the Castles in this video, however it was my intention to do this to three, but one had already been destroyed by an ally (the one closest to your start position). The other Castles that you should snipe from outside the walls are the one on the far left of the map and the one on the far right of the map. Your allies will potentially destroy the one closest to you, but this is not guaranteed. I found the best entry point to use is where you ally, Ataulf is. Follow him in and build a Castle as soon as he attacks and start pumping Trebuchets, but make sure to also upgrade your Huskarls as soon as you can as well as getting the two increased Barracks production speed upgrades. I try to destroy every Castle from a distance and engage in as little prolonged combat as possible. After breaching the wall, there is a Castle to the South you can kill with a Trebuchet(s) with little or no resistance. Then across the bridge to the East, there is another castle which can be destroyed with Trebuchets - again, with little or no resistance. Then, make your way South-east and destroy the Castle surrounded by water from a distance and follow up by destroying the next Castle just to the North-east of it. Now, you'll want to double back on yourself and head directly North of the gate that your ally, Ataulf originally destroyed and cross some shallow water to get round the back, destroying another castle on the way (just East of the shallow water). This Castle has a large army around it, but as you'll be destroying it from behind a wall rather than where the gate is, they shouldn't chase you. Continue North-east up the road to the Castle at the very North of the map, again keeping your distance as best you can to avoid taking any more casualties than needed and protect your Trebuchets. After this, continue following the road South-east and you'll come across another castle behind a wall with a gate. Destroy this one too and the final Castle on your journey with your main army is just to the South-east again and can be sniped from behind the Aqueduct. This route covers eight of the twelve Roman Castles. As previously mentioned, three of the other Castles (far West, far South and far East) castles can be destroyed by Trebuchets from outside the wall and the twelfth Castle will always be destroyed by your ally, the Visigoths and is located just West of their entrance.
Now you know the plan, let's discuss the start. Build at least four Town Centres and get a lot of Villagers on resources - You'll really need to boost your income as much as you can early on so that you can ignore it for the most part later on. Send your Light Cavalry to the South of the map and then to your ally in the West, Ataulf, and he will begin his assault. Don't send it directly to the West or it will go through an enemy encampment and likely die. Send the rest of your starting army North-east to the Visigoths straight away, destroying the towers and army along the way and they will begin their assault too. Make sure you have enough stone for the mid-game, so that you can build Castles on the far East and West of the map outside the walls and snipe the enemy Castles there with Trebuchets as well as sending one back to your start location or building a Castle there as well and sniping the Castle closest to your starting location. There is also one upgrade at your Blacksmith that can be had that will increase your infantry damage, which is worth getting as the army we'll be using will consist of just Elite Huskarls and Trebuchets.
The final word of advice I can give is be persistent. My first attempt took 45+ minutes, but I began trying a few different things and tweaking my movements here and there. In total, this took me around 15 attempts, but with each attempt, I could see my average time coming further down. On the score screen after this video, it said the play time was 30:05, so I had no time to spare (although I did almost forget about the Castle in the West)