Writer and director Christopher Nolan conceived the ideas behind Tenet over the course of twenty years, but began working on the script in 2014. The title, as well as being a palindrome, is an allusion to the Sator Square. Inspired by a feeling about how he imagined Sergio Leone made Once Upon a Time in the West (1968), Nolan avoided watching any spy films that might influence him while making Tenet, instead relying upon his memories.