Barbican is an advanced work before the gate of a castle or fortified town, or any outwork at a short distance from the main works, generally serving the purpose of a watchtower. There are barbicans remaining at York, Scarborough, Alriwick, and Carlisle castles. This term is especially applied to the outwork intended to defend the drawbridge, called in modern fortifications the tete du pont. It was frequently constructed of timber. It often consists of two-walls parallel to each other with an arch or a gate at each end to defend the principal gate, which is midway between them.