The Dowager Countess mentions that her cottage was designed by Wren. She is referring to Sir Christopher Wren (1632 - 1723), arguably the most famous British architect of all time. His most famous work is St. Paul's Cathedral in London. Coincidentally, Hugh Bonneville, who plays her son Robert Crawley (The Earl of Grantham) also played Wren in the TV documentary, "Wren: The Man Who Built Britain."
It's revealed that Mr. Bates served with Lord Grantham in the army years prior to his arrival at Downton. Oddly enough Brendan Doyle (Bates) and Hugh Bonneville (Grantham) portrayed shipmates on an English naval submarine in the James Bond film "Tomorrow Never Dies."