Although shooting commenced in Greece in November 1960 and the film was completed and copyright dated 1961, Fox seemed to be in no hurry to get it to the cinemas. After the Philadelphia premiere in August 1962, it was submitted to the British Board of Film Censors on 10 September 1962 and passed with a "U" certificate. The London premiere finally arrived on 25 October 1962 when it ran at the Rialto for a quite respectable five weeks. The UK general release at normal prices was from 11 November 1962.
There were supposed to be 5,000 extras for the battle scenes but in the end they had to make do with 1,100 (which meant that even if 250 soldiers had been assigned as the "300" Spartans, then just 850 doubled as the Persians. That number was supposedly added by more civilian extras (all those camp followers of the Persian army).
At the time, this movie was considered the most violent movie in America.