One of the easiest ways to attack your enemy in no time at all is using a Greek Assassin. These units can only be deployed against an enemy city and cause a one-time 12600 offensive output on your enemy's defenses in 3 minutes or less regardless of where your enemy's city is on the map. The Greek Assassin is destroyed after the attack. They are one of the only units in the game that requires drachmas to be able to purchase. The base cost is 500 drachmas.
Acquiring a Greek Assassin
To acquire a greek assassin, go to your market, select "Units", then select "Offensive"
Where to find your purchased Greek Assassins
Greek Assassins do not stay garrisoned in your city or in your acropolis. They are stored in the "Political Unit" section in your War Council. To get to the Political Unit section, click your War Council. Stay under the "City" tab, scroll all the way to the bottom (past "Units in Your Acropolis" and "Other Units in Your City") and you will find the Political Unit section. You can check how many Greek Assassins you have here.
How to use a Greek Assassin to Attack Your Enemy's City
There are two ways to use a Greek Assassin. You may go to their city on the map, and click the Green button to the left of the raid/besiege/dispatch scouts buttons.
You may also visit their city and deploy the Greek Assassin from there.
Deploy Multiple Assassins at Once!
When you order a Political Attack, the game will prompt you to select the number of Assassins you will deploy at once. If you have more than 1 available, you can select up to 10 to use at once.
You may send 10 political attacks in one day. Combine that with the maximum of 10 you can send at once, and you find that 100 is the maximum number of Greek Assassins that may be used in a single day.