You can't rewrite history! Not one line!
So spoke William Hartnell's Doctor, echoing a dictum that the First Doctor would return to again and again. "The Aztecs" is an important story not simply because it established that "rule," which would hold true for some time, but because this is the earliest Historical story that fully survives (indeed, only three "true Historicals" are currently complete in the BBC archives) and, as such, serves as our best example of Doctor Who's original approach to historical drama. In the "true Historicals," the Doctor and his companions are kept from the TARDIS somehow and (most importantly) there are no science fiction or fantastical elements present. The TARDIS crew must survive in the historical period by their wits and/or their strength. "The Aztecs" is a picture perfect template for this basic plot with a lot of wonderful details thrown on top. As I mentioned above, this was my introduction to the Historical story and it's a pretty good way to start.
A smaller scale (and budget, clearly) than Lucarotti's previous "Marco Polo," to be sure (though the closest I'd come to experiencing the earlier story was its Target Books novelisation), "The Aztecs" is in some ways a more complex story, specifically Barbara's quandry when she is mistaken for a goddess and tries to use her power to alter history (in her opinion--as Ian finally makes her realize) for the better. Her failure is preordained; the Doctor, implying he possesses hard-won knowledge, tells her as much early in the story. It's Barbara's struggle to understand that her sensibilities and those of the Aztec people are ultimately incompatible (a problem many historians occasionally fall into) that makes this serial really shine. Add to this the Doctor's "romance" with the Aztec woman Cameca and a fantastic villain in Tlotoxl (a villain who actually wins, having "defeated" Barbara's hopes!) and you get a story that feels just as vibrant to us today as it must have when it was first shown.
All right, enough of this late-night rambling. Everything specific we discussed (such as the brilliant scripting and excellent acting) in our episode posts:
"The Temple of Evil"
"The Warriors of Death"
"The Bride of Sacrifice"
"The Day of Darkness"
As always, here's a discussion of the writing and production of this story from the "Brief History of Time (Travel)" site and here is a link to the official BBC episode guide for the story. Check them out for facts, historical critiques, etc.!
And, in a few days, we'll return to science fiction as we get closer and closer to the end of the first season....Until then, I remain