The Fourth Dimension
The Wedding of River Song
The Doctor hears about the death of his old friend, Brigadier Alastair Gordon Lethbridge-Stewart. The character was played by Nicholas Courtney who died earlier this year. You can find out more about the role he made so memorable and eternally popular here.
This isn't the first time pterodactyls have appeared in Doctor Who. The Third Doctor and Sarah Jane survived a pterodactyl attack in the 1974 adventure, Invasion of the Dinosaurs.
'The death of time' is referred to by Madame Kovarian in the pyramid. The Death of Time was the second episode of the First Doctor adventure, The Chase. Incidentally, episode 5 of this 1965 story features a robot that looks exactly like the Doctor...
Cleopatra is again mentioned but remains unseen. Mickey Smith revealed the Doctor knew Cleopatra and River later impersonated her. The Fourth Doctor himself claimed to have learnt his skills with a sword from one of her bodyguards.
Napoleon (Napoléon Bonaparte, 1769-1821) is also referred to. In Day of the Daleks, the Third Doctor remembers how he called him 'Boney' and advised him that an army marches 'on its stomach'. Unlike Cleopatra, Napoleon has made an appearance in Doctor Who, meeting the Time Lord's companions in The Reign of Terror.
Queen Elizabeth I (1533 -1603) is also mentioned. She appeared in The Chase and The Shakespeare Code and the Tenth Doctor implied he knew her very well.
'I just climbed out of the Byzantium.' River is referring to events we witnessed in The Time of Angels/Flesh and Stone, although we first heard her allude to the starliner during Silence in the Library.
Mark Gatiss returns to the world of Doctor Who, this time playing Gantok. He last appeared in the show playing Doctor Lazarus in the Tenth Doctor adventure, The Lazarus Experiment.
Other notable returns include Simon Callow, reprising the role of Charles Dickens, last seen in The Unquiet Dead; Richard Hope, back as a Silurian doctor after first appearing in The Hungry Earth/Cold Blood and Ian McNeice, once again playing Churchill. Off camera, Nicholas Briggs again voices the Dalek.