The gather rate of rare resources can be increased in various ways, as described in the main article. Note that Knowledge is not gathered before the Classical Age, but the Greeks may gather Knowledge from the beginning, making an early exploitation of Spice more useful.
The bonus on Caravan income is nothing too sensational, increasing a caravan's Wealth gather rate by something like +1 to +5 (per 30 seconds), depending on the length of the trading route. For instance, Caravans plying routes between neighboring cities generate an addtional +1 to +3 Wealth, while higher bonuses of +5 and more require a trading route roughly across half a standard map. The Persians are more likely to take full advantage of this rare resource as their Caravans are automatically produced.
- Spice's Knowledge boost is attributed to the science of cultivating spices for maximum yield or potency.