Complete "Under Pressure" with the Pro Persian Civilization.
After completing Gaumata's Gambit for Darius in your home city, this will be one of the next complete able quests. In order to succeed, you must reaching 200 population (and a bonus for 100 of that being villagers).
The quest can be done at the starting level (20) as long as you prepare yourself quickly upon entering the quest by walling a vertical rectangle around your city. It is important that you wall from the Southern tree line on the SE and SW side of the side, up the sides and a ways North of your capital building. In the mean time, create a large number of villagers and queue up age 2 at the end of the queue, and send those villagers to the farthest rock harvest point within line of sight of your town (there should be two just NE of your town, if there aren't you may want to consider restarting until there are), have some villagers collecting the gold point to the West, and send villagers down to South to start harvesting the tree lines. Upgrade your walls immediately as well, defense is absolutely key for this quest as you will be constantly under attack, primarily from the East and North, with a few attacking from the West every now and then, so walls and later a couple of fortresses defend you without the population losses suffered by using soldiers. If possible, put up buffer walls as well, however saving stone for 3 more town centers, and about 3 Fortress (North OR East first, then one on the West after those 2 are up). The use of Town Centers to help defend the walls is smart as well, I put my first one along the West wall and pretty much pacified any major damage that could have come against my wall.
Be sure to constantly pump out villagers from every town center you own until you are about to cap your optional quest, and then build around 4 barracks, and have the first one research the skill that lowers recruitment time. At this point you will probably be sub-10min with your walls hopefully still standing and your last fortress up or about to be coming up. Continue to pump out villagers, and now begin to fill the barracks queues as well until you have won the battle. Once you learn to handle the attacks from the N/E, the quest is relatively simple.