Deliberate mistake: Wooden crosses are shown in several scenes, hanging on a wall. Crosses did not come into use as a Christian symbol until 450 A.D. (about 400 years after the film is set).
Deliberate mistake: Before Blanche's birthday dinner, she comes out of the bathroom with her wet hair up in a towel and asks Stella for another towel saying she's just washed it. Moments later she emerges from the bathroom with completely dry and styled hair that would have taken hours to do during that time period.