Anne Brownlow, Lady Cust (1694-1779), the mother of Sir John Cust, insured Grantham House for £1,000 in 1768 (£180,000 2021). The Sun Fire Office fire mark recording the insurance is located on a north wall, red circle. By using the number embossed on this lead fire mark, 259606, we traced the original policy registration document to the London Metropolitan Museum, transcribed below. The Sun Fire Office is the oldest documented insurance company in the world. It was founded in London in 1710. It continues to trade under RSA Insurance Group Limited, formed from the merger of Sun Alliance and Royal Insurance in 1996.