Goblin Slaves’ Entrance

There were about a dozen goblins assigned to do the task. They chose an area about a few hundred meters away from the walls, hidden from the line of sight of the unfamiliar weapons. After a bit, the goblins began to dig a tunnel towards the wall at an unprecedented pace. 

The little ones were small and perenially frowning. Their backs were hunched from working so much, making them appear even smaller, but their arms worked fast as they dug. 

They also knew where the weak spots of the soil were as if they could see it clearly, so even if they weren't so strong, the soil tended to appear softer than it would if a human was doing the same task. 

Goblins were fast diggers, let alone dozens of them, and they were able to create meters-long tunnels fit for a few people twice their size within several minutes.