Mixed Defence City

This guide should give a good example of what kind of "Mixed Defence Cities" you can create. You may or may not have to build the entire thing like with you first city, you might be able to take down a nice sized city and just convert it into whatever you'd like. for this guide, we will be converting a city into a "Mixed Defence City".

First of all, I should remind you of a few things such as converting researches in the Academy. You can get rid of whatever researches you would like by going to the upper right-hand corner of the academy and selecting "Reset", but remember that for every research you reset, it costs you 1 "Culture Point", so keep that in mind.

Secondly, you want to think about what kind of 'Mixed Defence City" you want to create based on what you expect from your enemies. If there are allot of Harpie or Manticore nukes, then you might want to consider a "Manticore/Harpie Trap". If you still would like to create a "Mixed Def City", then you do not have to go all balanced, you could emphasize the archers, or the hoplites to give you an edge against those nukes. But of course the most basic "Mixed Def City" is a well balanced one, especially early in the game before Grepolis starts any events (Things like the Golden Hen during Easter, where you can feed your golden hen to receive different rewards from whatever the hen lays), or just after and in between events where no one is winning several Manticores, and Harpies.

Build: 

Academy:

Research:
Slingers,
Archers,
City Guard,
Hops,
Villager's Loyalty (Formerly called Diplomacy),
Booty,
Ceramics,
Architecture,
Trainer,
Biremes,
Crane,
Shipwright,
Conscription,
Colony ship,
Fast Transports,
Plow,
Bunks,
Phalanx,
Mathematics,
Battering Ram,
Cartography,
Conquest,
Battle Experience,
Strong Wine
you will then have 10 research points remaining to do as you please.

Buildings:

Maxed:

Farm,
Timber Camp,
Quarry,
Academy,
Wharehouse,
Wall,
Cave,
maybe Temple

Others: 

Senate 10-15 (demolish to 10-15 after getting Baths and completing most needed buildings),
Silver Mine 20,
Barracks 15,
Temple 15-max,
Harbour 20,

Special Buildings:

Baths on the left, and Tower on the right (You could if desired build different but this is the safest route).

Army/Navy:

Basic Mixed Def.:

Random Suggestion:
150 Swords, 315 Archers, 255 hops, w/ 100 slinger or 35 Horsemen.
As for the Navy you'll want:
200-300 Biremes, and 45 Fast-Transports.

You can break this down into 5 units, to send support to 5 different cities per city (30swords/63archers/51hops/50BIR/9FT).

Balanced (10260 against each blunt, sharp, and ranged): 
180 Swords, 180 Archers, 360 hops, w/ 50 slinger, and around 20 horsemen for quests.
As for the Navy you'll want:
200-300 Biremes, and 45 Fast-Transports.

You can break this down into 5 units, to send support to 5 different cities per city (36swords/36archers/72hops/50BIR/9FT).

Advanced Mixed Def.:

God: Athena
Just add 10-30 Pegasus (200-600 FS), would go a long way against harpies. 10 Pegs will kill 50 harpies w/ a level. 20 wall, and a Tower, 30 will kill 150.

Also, you could make about 20 Centaurs (240 FS) in 3 different mixed def. cities which combined will save any Athena cities from just about any Harpie attack by themselves (45 centaurs kill 50 Manticores with level. 20 wall and tower). 

God: Artemis
Just add 20 Calydonian Boars to two or three different mixed def. cities and combined they could def. almost any Manticore or Harpie nuke (35 Boars kills 50 Manticores, it also kills 175 Harpies). You would be allot safer with these in your arsenal.

Summery:  Hera, Zeus, and Hades

Myth units such as Medusa, are more balanced and could be used in a balanced def. strategy, also there is Cerebus who is good against Harpies (blunt attacks), and yet greater against ranged. If you have a problem with slinger/catapult nukes (Demo nukes), then add a few Cerebus with Hades as your mix def cities God. As for Zeus's Minotaur, these are good but not great def myth units, by far the most mediocre myth def. unit. I still like about 5 of these to help defend my Manticore nukes, though.