The Professor's first stop this week is at the Leighton House Museum. It was the former home and studio of the leading Victorian artist, Frederic, Lord Leighton. He bought it for just £4500 in 1866, slowly adding and extending it. Next, Professor Hutton pays a visit to The Museum of the Order of St. John. Based in St. John's Gate, the building is a 16th century gatehouse that once formed the entrance to the much older Priory of Clerkenwell, once the English headquarters of the 11th century Order of St. John who went out to Jerusalem as part of the Crusades.

• Ronald Hutton