Economy
For most factions, the majority of wealth flows from trade. Trade is done overland and by sea, the naval method being by far the more lucrative. You cannot trade with factions you are at war with, but otherwise trade flows normally. Negotiating trade rights increases the revenue for both sides.
Thus, in general the richest lands tend to be those around the Mediterranean, particularly Greece, southern Italy, the islands of Crete, Rhodes and Cyprus, and the eastern Mediterranean in general, where provinces are numerous.
Each city is limited in the number of trade fleets by the size of its port. A Port has one fleet (ie, export connection to another city), a Dockyard has 2 and a Shipwright 3.
Affecting the revenue from land is the quality of roads. Roads not only make travel for armies faster, but they increase overland trade. Regular roads are hardly better than no roads, paved roads somewhat of an improvement and highways – which are exclusive to Rome – give the biggest boost.
Finally, all trade benefits from larger markets. A small trader cannot compete with a Market, which in turn upgrades into a Forum and so on. Different factions have different names for these.
The biggest disparity between barbarian and civilized forces is not the quality of troops, but the difference between economies. Barbarian cities cannot have anything but regular roads, and their city improvements are limited to only the third level. This means no fancy markets, no aqueducts to keep the population healthy and growing, and even no stone walls in most cases.
Unlike previous Total War games, trade isn’t only between states. Now, cities within the same empire can deal with each other. This speeds the growth of large nations, since they become less dependent on trade treaties and peace for profit.
Navies are much less important in maintaining economy since trade is independent of where the player has ships. However, ships can blockade ports. Though the AI is haphazard in using its navies and blocking enemy ports, the player should take the opportunity to build up his fleet and starve the enemy into submission. Macedon, Greece, Egypt, Pontus, Carthage and the Seleucids are particularly dependent on trade and thus vulnerable to blockades.