Revealing mistake: During the scenes involving heavy rocks and boulders rolling, crashing, smashing, launching, etc, it is obvious they are made of lightweight material due to their bouncing off each other, the actors, the sand, etc.
Masada (1981)
1 revealing mistake in show generally - chronological order
Starring: Peter O'Toole, Barbara Carrera, Peter Strauss, Alan Feinstein
Revealing mistake: After Lentius stabs Silva, the knife blade Lentius used bends and wobbles as it is thrown to the ground.
Cornelius Flavius Silva: A victory? What have we won? We've won a rock in the middle of a wasteland, on the shores of a poisoned sea.