It’s a huge tale focused on the brutal historical confrontation between Spanish conquistador Hernando Cortez* and Aztec leader Montezuma in 1519 after the former led an incursion into Mexico. Pushing through the area looting the riches and bringing smallpox and disease in his wake, Cortez was eventually captured and held as a prisoner/guest by Montezuma. He managed to turn the tables, though, making the Aztec leader his puppet as his forces began devastating attacks on the Aztec population, leading to Montezuma’s death at the hands of his own countrymen. Later, it appears that he fathered a son on Montezuma's daughter after she had been converted to Christianity, married to a series of Spanish noblemen and widowed several times.
Trumbo – famously one of the Hollywood Ten who refused to testify at the communist-hunting House Un-American Activities Committee and landed in jail for 11 months – endured pariah status until Kirk Douglas and the producers of Spartacus hired him for the film. The pair formed a close working relationship and Trumbo wrote Montezuma for Douglas to star in around 1965, but the film never came together.
Now Bardem is considering playing Cortez (and the story, which takes his point of view despite the title, could be renamed), with Zaillian at work on a re-write.
According to Deadline it’s too early to tell if Spielberg will make this his next film, and it’s not really far enough along to suddenly clank into production, but it is an intriguing possibility for the future. Spielberg's one of the best there is at bringing historical sweep to life, and the clash of cultures in the early exploration of the Americas by Europeans seems ripe for drama. Bardem, meanwhile, seems like a great fit for the disaster-prone Cortez.
* More properly Cortés and Moctezuma, but we'll go with the film's spelling.