A medieval barn near Heathrow Airport, built between 1426 and 1427 for Winchester College, has survived for over six centuries despite weather and historical changes. The barn is 58 meters long and was constructed using a method where its parts were assembled on the ground before being raised into place. This technique, along with the materials used, has helped the structure remain intact. Dendrochronology, a method that dates wood by analyzing tree rings, confirmed that the main carpentry was completed between the winter of 1424-1425 and the spring of 1426. It is believed to be the largest medieval wooden barn in England still standing. Originally, the barn was used to store grain from the lands owned by Winchester College, including wheat, barley, oats, peas, and beans. In 1544, it was taken over by King Henry VIII and added to his personal hunting grounds. The property was later sold in 1547 to the Paget family, who kept it for more than two centuries. In 1774, the north wing of the barn was demolished, but the remaining structure has endured the passage of time. Situated in Harmondsworth, Middlesex, the barn is part of a group of the best-preserved medieval barns in Europe. Poet John Betjeman once referred to it as the "cathedral of Middlesex" because of its architectural similarity to a religious building. The barn's survival is largely due to the skill of its builders and the materials used, including ferricrete walls—made from a type of hardened clay—and locally produced tiles. Despite the modern environment of Heathrow Airport, the barn continues to stand as a remarkable example of medieval engineering and durability.