An L-plan castle is a castle or towerhouse in the shape of an L, typically built in the 13th to the 17th century. This design is found quite frequently in Scotland, but is also seen in England, Ireland, Romania, Sardinia, and other locations. The evolution of its design was an expansion of the blockhouse or simple square tower from the Early Middle Ages. As building techniques improved, it became possible to construct a larger building footprint and a more complex shape than the simple blockhouse tower. A more compelling motivation for the L plan was the ability to defend the entrance door by providing covering fire from the adjacent walls. This stratagem was particularly driven by the advent of cannon used by attackers.