The TARDIS lands in 1289 China. There it is seized by explorer Marco Polo, who intends to present it as a gift to Kublai Khan, in the hope that it will win him his freedom. The Doctor, Susan, Ian and Barbara will have to accompany Polo as he travels across the desert to the court in Peking. Susan befriends a young girl in the caravan named Ping-Cho, who is heading towards an arranged marriage. Also accompanying Polo is Tegana, an emissary of a rival warlord. While claiming to seek peace with Kublai Khan, Tegana's true mission is to assassinate the Khan, imperilling the lives of Polo and all those journeying with him.

Before moving to Britain, Doctor Who creator Sydney Newman had made a name for himself at the Canadian Broadcasting Corporation. There, he met English writer John Lucarotti, who had been supplying scripts for the CBC since the mid-Fifties, including a lengthy 1956 radio serial entitled The Three Journeys Of Marco Polo. In 1963, Newman recommended Lucarotti to Doctor Who story editor David Whitaker. By this time, the writer had taken up residence on a houseboat moored at Majorca, off the coast of Spain, but returned to London in late June of that year to meet with Whitaker and producer Verity Lambert.

Lucarotti was interested in writing an historical adventure for Doctor Who and suggested it might involve the Venetian explorer Marco Polo. This narrative would allow him to make use of the material he had compiled while researching his earlier radio serial. One of history's best-known explorers, Polo left Venice in 1271 to accompany his father and uncle to the palace of Kublai Khan at Shangdu, China (which Europeans knew as “Cathay”). Polo impressed the Khan and travelled extensively throughout Chinese lands at his behest; he also served as the Khan's emissary to India and Burma. However, the Polos had become too useful to the Khan, who repeatedly denied them permission to return home. He finally acquiesced around 1291, and the Polos returned to Venice via Constantinople in 1295. About a year later, Polo was captured during a war with Genoa and narrated his exploits to a fellow inmate, Rustichello da Pisa. Polo grew famous across Europe when Rustichello compiled these memoirs into a book, which became known as The Travels Of Marco Polo (originally The Wonders Of The World or Description Of The World).

The route followed in the serial was inspired by Marco Polo's original journey to Shangdu, around 1275

Lucarotti's serial, “A Journey To Cathay” was commissioned on July 9th. In crafting his scripts, Lucarotti drew heavily from Polo's memoirs. The route followed in the serial was inspired by Polo's original journey to Shangdu, which culminated around 1275. Ping-Cho was inspired by a real-life figure, the young Princess Kököchin, whom Polo escorted to Persia in 1293. The Princess was betrothed to the Khan's great-nephew, Arghun, who was nearly twice her age. Upon their arrival, however, they discovered that Arghun had passed away, and Kököchin instead married his son, Ghazan. This was indeed Polo's final service to Kublai Khan before being granted permission to return home.

Tegana, Acomat and Noghai were all named for Tartar rulers mentioned in Polo's memoirs. Many of the historical facts included by Lucarotti in his scripts -- such as the descriptions of the Khan's stables -- also came from The Travels Of Marco Polo. Unusually, Lucarotti proposed an animated map and voice-over narration to help evoke the long journey. Originally, it was intended that the narrators would be the Doctor, Ian and Barbara, before it was decided instead that these should represent extracts from Marco Polo's diaries.

“A Journey To Cathay” was originally intended to be the third Doctor Who story. However, in late October, budgetary concerns prompted the refusal of Donald Baverstock, the Controller of Programmes for BBC One, to authorise the series' continuation beyond its initial thirteen-episode run. Since Lucarotti's adventure was preceded by 100,000 BC (four episodes) and The Daleks (seven episodes), the potential existed for the programme to be cut off midway through the Marco Polo serial. As such, the two-part Inside The Spaceship was commissioned to be made and broadcast after The Daleks. The production of “A Journey To Cathay”, now fourth in the schedule, was finally green-lit by Baverstock on November 22nd, when he ordered a second block of thirteen episodes.

The director assigned to “A Journey To Cathay” was Waris Hussein. Hussein had previously handled 100,000 BC and it was originally intended that he would alternate serials with Rex Tucker throughout the season. Despite the shifting of Lucarotti's story in the running order, Hussein remained attached as director, although it was briefly thought that junior director Richard Martin (who had gained experience on both The Daleks and Inside The Spaceship) might handle the fourth and sixth installments.

Five days of filming began on January 13th, 1964 at the BBC Television Film Studios in Ealing, London. Various scenes were completed, most notably Polo and Tegana's sword fight in the throne room, as well as those involving significant quantities of water. As with 100,000 BC, Hussein allocated some of the filmed material to production assistant Douglas Camfield, who would soon be promoted to director himself, and was later prolific on Doctor Who.

When William Hartnell fell ill, part two was restructured to minimise the Doctor's role

Studio recording then got under way at Lime Grove Studio D at Shepherd's Bush, London on January 31st; each episode would be taped there on successive Fridays. William Hartnell fell ill the following week and so part two, The Singing Sands, was restructured to minimise the Doctor's role. In particular, an opening scene involving Susan and Barbara replaced a version with Susan and her grandfather. A small error occurred when the “Next Episode” caption used at the end of the installment referred to “The Cave Of Five Hundred Eyes”, even though part four's title had already been abbreviated to simply Five Hundred Eyes.

On February 20th, Doctor Who featured on the cover of the Radio Times listings magazine for the first time, although the debut episode of 100,000 BC had originally been slated to receive this treatment the previous November. The black-and-white photograph featured Hartnell with guest stars Mark Eden and Derren Nesbitt, who played Marco Polo and Tegana, respectively.

Unique of all the episodes of Marco Polo, The Wall Of Lies -- recorded on February 21st -- was directed by John Crockett, a former designer. Crockett was so invigorated by the task that, on February 26th, he wrote a memo to Whitaker suggesting a number of possible historical settings Doctor Who might pursue. Of these, the Viking raids on Britain, Bonnie Prince Charlie, the Crusades, Catherine de Medici, and Cornish smugglers would all eventually be employed in some form or another (though Crockett's influence is doubtful).

On February 22nd, William Russell spoke with his agent, T Plunkett Green, about his recent frustrations with Doctor Who. Russell felt that he and co-stars Jacqueline Hill and Carole Ann Ford had been slighted by their omission from the Radio Times cover in favour of two guest performers. Russell was also unhappy with six minutes of new scenes which had been added to The Wall Of Lies on the final day of rehearsals. On February 28th, Head of Serials Donald Wilson responded to Plunkett Green after discussing the matter with Verity Lambert. They sympathised with Russell's concerns, and agreed that all of the regular castmembers would be more closely consulted about scripts in the future.

February 28th saw the recording of episode five, Rider From Shang-Tu. Matters were complicated by the presence on set of a spider monkey which, in the narrative, belonged to the thief Kuiju. The animal hired for the purpose was not a trained performer; becoming terrified by the experience, it spent much of the day loosing its bladder and bowels around the studio, and work was delayed when it escaped into the rafters.

A delay in recording the serial's finale exacerbated frustrations with Lime Grove Studio D

The taping on March 6th of the sixth installment, Mighty Kublai Khan, was preceded by a remount of the closing scene of part five. Around this time, the serial was renamed Marco Polo. On the 13th, recording for the serial's finale, Assassin At Peking, was delayed when the fire marshal voiced concerns about the positioning of some extraneous equipment in Studio D. This situation further exacerbated the production team's frustrations with Doctor Who's home at the antiquated Lime Grove facility. On March 18th, associate producer Mervyn Pinfield wrote to Wilson to complain that the cramped conditions of Studio D were being made worse by its apparent use as a storage facility.

On March 9th, Lambert was informed that her request to shift Doctor Who's timeslot back by fifteen minutes, to 5.30pm, had been granted. This would take effect with Mighty Kublai Khan on March 28th, and meant that Doctor Who would now follow the second season of The Telegoons in the BBC TV schedule, while still preceding Juke Box Jury.

• Doctor Who Magazine #240, 3rd July 1996, “Archive: Marco Polo” by Andrew Pixley, Panini UK Ltd.
• Doctor Who Magazine #483, March 2015, “The Historic Journey Of Marco Polo” by Patrick Mulkern, Panini UK Ltd.
• Doctor Who Magazine Special Edition #7, 12th May 2004, “Do You Want To Know A Secret?” by Andrew Pixley, Panini Publishing Ltd.
• Doctor Who: The Complete History #2, 2016, “Story 4: Marco Polo”, edited by John Ainsworth, Hachette Partworks Ltd.
• Doctor Who: The Handbook: The First Doctor by David J Howe, Mark Stammers and Stephen James Walker (1994), Virgin Publishing.
• Doctor Who: The Sixties by David J Howe, Mark Stammers and Stephen James Walker (1992), Virgin Publishing.