Power Buildings

The caravan isn't a useless thing, because you wander around the map and find a lair of monsters, capture them, and hire them. However, it's located two days away (assuming the army's speed is less than 30). Then you build a caravan, and you can hire these monsters, and they will immediately be in your city on the next turn. So, it's not that useless. And let them lose. But IMHO, they are better than harpies. Because I always took them when I had 4 creatures, and I got used to the fact that they aren't as strong as harpies. But now it's uncomfortable for me to play with harpies.