Final answer:
Alfred the Great defended his kingdom of Wessex from Viking invasions by fortifying cities, building a system of burhs, establishing the fyrd, implementing reforms in defense and governance, and promoting education and learning.
Step-by-step explanation:
When the Viking Ivar and the "Great Heathen Army" took York, Alfred the Great defended his kingdom of Wessex by fortifying his cities and building a system of burhs, or fortified towns. These burhs were strategically placed to protect the kingdom from Viking invasions, and they provided a safe haven for the people during times of attack. Alfred also established a professional standing army called the fyrd, which was composed of trained soldiers who could quickly respond to Viking raids.
Additionally, Alfred implemented reforms in his kingdom to improve the overall defense and governance. He established a navy to protect against Viking fleets, built a network of roads to allow for faster communication and troop movements, and encouraged the production of weapons and armor. Alfred also fostered a system of education and learning, promoting literacy and intellectual pursuits to strengthen his kingdom's cultural and intellectual resilience.