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.
For most of human history, international trade was based on several commodities: slaves, gold, silk...and spices. Of these, spices were probably the most significant. With salt and spices, food could be preserved and kept for longer periods, or at least have the taste of spoilage concealed with strong flavours, with the most desired spices in Europe being pepper, cinnamon, saffron and ginger.
In the Middle Ages, the Venetians enjoyed a near to unrivalled domination of the spice market through their ties with the (formerly Roman) Byzantines and (later) the Mongols. Spices, however, were also the catalyst for global Western imperialism as following the fall of Byzantium in the late 15th century, the old trade routes to India and the Malay Archipelago (the primary sources for spices) were cut and European powers began to seek ways to circumvent them.