The portle is the barred door that usually closed castles, fortresses "Fortress (architecture)"), fortresses and other buildings in the Middle Ages. It was one of the defenses of the main gate, along with the drawbridge and the barbican, being one of the last lines of defense against attacks and sieges.

It is a lattice "Lattice (architecture)") of wood, metal or a combination of the two, which is mounted on vertical slots in the castle walls and which can be raised or lowered quickly by means of chains or ropes attached to winches and even counterweight systems.

There were often two portcullises at the main door, the one on the inside was closed first and then the outside, thus being able to trap the enemy and, sometimes, burning wood and pitch or fire-heated sand were dropped on them from holes in the roof. Hot oil, however, was not commonly used, contrary to popular belief, as it was extremely expensive.[1] There were often loopholes in the side walls, allowing archers and crossbowmen to eliminate the trapped group of attackers.

In England, portcullises that have survived in operation are found at the Tower of London, Monk Bar in York, Amberley Castle and Hever Castle.