There were gateways through the curtain wall at a number of places. First, there were the gates at (nearly) every milecastle. At least one (Milecastle 35) had none, since it was perched on the edge of a cliff. It is also assumed that there were gateways at each point where a major road passed through the Wall. One of these, at Portgate, where Dere Street crossed the Wall, has been partially excavated and others, near Carlisle to the west and Newcastle to the east, may have existed. Once the forts were added, these also included gates, although it is unknown whether passage through the Wall was permitted for non-military traffic. The existence of the Knag Burn gateway adjacent to the fort at Housesteads makes that unlikely and it may indicate that some gates were inserted for reasons that are no longer clear, perhaps in this case connected with transhumance.