Fishergate Postern Tower

Fishergate Postern Tower was built between 1504 and 1507, replacing an earlier tower on the same spot. In the medieval period the river Foss lapped at the foot of the tower. The postern, or small gate, next to the tower had its own portcullis (a heavy wooden gate, shod with iron which was lowered from above). Can you see the vertical slots it ran in?