Spice is one of 31 Rare Resources in the game and available from the beginning. It appears as a small group of spice plants with some bowls next to it. Like all rare resources on land, it can be obtained by sending a Merchant from the Market to the resource location. Spice provides the following benefits:Classical Age. However, the Greeks may gather Knowledge from the beginning, making an early exploitation of this resource 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. I.e., 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.