Windsor Castle is widely recognized as the oldest and largest occupied castle in the world, with a history spanning over 1,000 years. Founded by William the Conqueror in the late 11th century (around 1070), it was originally built to protect Norman dominance around London and overlook a strategic part of the River Thames. Over the centuries, it has been the home of 40 monarchs, including the current King Charles III. While other ruins might date back further, Windsor remains the gold standard for an "intact" and functioning royal residence. Another contender for the title of "oldest stone castle" is Chepstow Castle in Wales, which began construction in 1067. These fortifications serve as a physical timeline of British history, evolving from wooden motte-and-bailey structures into the grand stone fortresses seen today.