All-Star Cast: Patrick Stewart, Liam Neeson, Gabriel Byrne, Helen Mirren, Nicol Williamson, and Ciaran Hinds. This is actually an inversion, as none of them were especially big at the time, at least not in the United States, and Boorman chose them because they were relatively unknown and didn't want big stars to overshadow the production, Which makes this Hilarious in Hindsight.
Dawson Casting: Nigel Terry was 35 playing Arthur from a teenager to a 20-to-30-something king, and then finally as an old man. Similarly, 29-year old Cherie Lunghi played Guinevere from teenager to full adult queen to an old woman living out the rest of her life in quiet misery as a nun.
Deleted Scene: The original cut of the film was over three hours long. Among the many scenes that were lost was a scene (briefly glimpsed in the trailer) where Lancelot rescues Guenevere from a forest bandit.
Director John Boorman originally wanted to do a film adaptation of J.R.R. Tolkien's The Lord of the Rings trilogy, compressing the trilogy into one very long film, but he couldn't get the rights to it so he made Excalibur instead. Reportedly his screen treatments sexed up Tolkien's story quite a bit, including but not limited to giving Frodo Baggins pointless nude scenes he didn't have in the books and having the House of Healing scene between Eowyn and Aragorn feel like a sex scene (as he planned to cut out Arwen and have Eowyn settle down with Aragorn, which reportedly was Tolkien's original idea). Generally the Arthurian myth sounds like it was better suited to him than Tollkien!