Burhs were fortified settlements built in England during the late 9th and early 10th centuries, primarily under the rule of King Alfred the Great. They served as defensive structures against Viking invasions and were strategically located to protect key areas and trade routes. These structures typically featured strong walls, gates, and watchtowers, allowing for better surveillance and defense. The design of burhs encouraged the growth of surrounding communities, as they provided safety and stability, leading to increased trade and population in the region.