To get this you need to head to the Imperial City which is in the middle of Cyrodiil. Once you have made it to your alliance's base via the sewer entrance, a general should give you a quest called "city on the brink", in which you only need to find and speak to the Drake of Blades. After that head to the room with the banker and the ladders leading up to each of the six districts. At the top of each ladder you will be given a quest for that specific district. Once you have cleared all six districts you get a seventh solo quest called "the sublime brazier." Complete that quest to unlock the achievement.
-You can only have one district quest active at a time.
-The house icon in each district will change from black to white once the quest is completed.
-Some of the quests can easily be completed solo, but having a group with you can make them considerably faster.
-You will likely need a large group to beat the Arena district.
-The Nobles district quest can get bugged from time to time, and the only fixes I found are to wait until that campaign cycle restarts or try a different campaign.