In 1430 South America, Barbara is mistaken by the Aztecs as the reincarnation of the High Priest Yetaxa. Now regarded as a living deity, Barbara realises that she could change history and end the Aztec practice of human sacrifice. But while Barbara has the loyalty of Autloc, the High Priest of Knowledge, she is mistrusted by Tlotoxl, the High Priest of Sacrifice. Scheming to disprove Barbara's divinity, Tlotxl kindles a rivalry between Ian and a mighty Aztec warrior, and ensures that Susan is chosen to wed a sacrificial victim. And how will the Doctor react to Barbara's decision?

On December 31st, 1963, the Controller of Programmes for BBC One, Donald Baverstock, consented to a further ten episodes of Doctor Who, beyond the twenty-six to which he'd already agreed. A month and a half later, on February 13th, 1964, the green light was finally given for the entirety of the programme's fifty-two-week production calendar. Shortly thereafter, during the production of Marco Polo, story editor David Whitaker asked that serial's writer, John Lucarotti, to tackle another historical adventure for later in the year, one which would mark the beginning of the newly-approved second half of Doctor Who's season.

Whereas Marco Polo had sprung from Lucarotti's research for a Canadian programme several years earlier, his ideas for his new story, The Aztecs, were inspired by a period of time he had spent living in Mexico. During his stay there, Lucarotti had become fascinated by the Aztec culture. In particular, he was astounded by the sharp contrasts inherent in that society, which had made enormous strides in astronomy, medicine and agriculture and yet forged no metal weapons or tools, was ignorant of the potential of the wheel, and practised human sacrifice. Lucarotti felt that the dying days of the Aztec civilisation, decimated by the forces led by Spanish explorer Hernando Cortes in 1521, would be the ideal setting for a more character-driven drama than Marco Polo had been.

John Lucarotti wrote The Aztecs on his houseboat in Majorca

The Aztecs was commissioned on February 25th. As with his earlier scripts, Lucarotti wrote the new serial on his houseboat in Majorca, Spain, travelling to London to meet with Whitaker when necessary. He avoided a lot of explicit references to the gods of Aztec mythology. Quetzalcoatl, the feathered serpent who was the god of the air and of learning, was described by Tlotoxl as “him who has fallen”. Huitzilopochtli, the southern hummingbird who was the god of war, was called “him who has made us strong”. Only Tlaloc, the rain god, was referenced by name.

Shortly before The Aztecs was added to the schedule, it had been agreed that each of the regular Doctor Who castmembers would enjoy a two-week holiday during the remainder of the season. Consequently, Lucarotti was informed that Carole Ann Ford would be absent from the recording of the second and third episodes of The Aztecs. Whereas the preceding serial, The Keys Of Marinus, had dealt with William Hartnell's vacation by simply excluding the Doctor from two installments, it was agreed that Lucarotti should instead minimise Susan's involvement so that her material could be pre-filmed prior to Ford's departure.

The director assigned to The Aztecs was John Crockett, who had earlier handled part four of Marco Polo. Two days of filming took place on April 13th and 14th at the BBC Television Film Studios in Ealing, London. On the first of these, Ford recorded a scene for each of the two middle episodes. The other day was used for filming the fight between Ian and Ixta, as well as the Perfect Victim's fall to his death.

In designing the serial, Barry Newbery had become concerned about Crockett's ability to realise the Aztec city. Newbery wanted to use a painted backdrop to provide a sense of scale, but the narrow confines of Doctor Who's usual production home in Lime Grove Studio D at Shepherd's Bush, London meant that such an approach was likely to be unconvincing on camera. Crockett requested a transfer to Studio 3 or 4 at BBC Television Centre in White City, London but was denied. As such, part one of The Aztecs, The Temple Of Evil, was scheduled for Studio D on May 1st. As usual, the remaining installments would be recorded on succeeding Fridays.

For weeks, Verity Lambert had battled to move Doctor Who to a more modern studio

However, Newbery's concerns were a microcosm of the frustration which had been felt by the Doctor Who production team since recording on the programme had begun in September. Not only was Studio D very small, but much of its technology was outdated, props and scenery had to arrive via a small lift, it tended to be uncomfortably warm, and it was even used to store spare equipment. For weeks, producer Verity Lambert had battled to move Doctor Who to more spacious and modern confines. On April 30th, John Mair of the BBC's Planning Department agreed that the programme should instead use Lime Grove Studio G and TV Centre Studios 3 and 4 whenever they were available. Lambert, however, viewed this as only a partial solution, since the unusually long and narrow proportions of Studio G would make it impossible to achieve the vast sets that Doctor Who frequently demanded. The debate would continue.

Nonetheless, this meant that the middle episodes of The Aztecs could be relocated to TV Centre Studio 3 after all. Unfortunately, the taping of part two on May 8th was marred by the discovery that the scenery for the base of the temple had been broken up in error. Newbery hastily made use of whatever extra materials were at hand -- such as elements of Susan's cell, which had been needed only for the pre-filming -- together with rented plants, thereby creating an impromptu “new” area of the Garden of Peace. The Aztecs returned to Lime Grove Studio D for its concluding installment on May 22nd. Temperatures were mounting with the approach of summer and, as if to welcome back the cast and crew, the studio sprinkler system promptly discharged.

• Doctor Who Magazine #266, 1st July 1998, “Archive: The Aztecs” by Andrew Pixley, 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 6: The Aztecs”, 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.