In the movie, Forrest receives an envelope from ‘Apple’ in 1975. ‘Apple’ became a public traded company in 1981.
Russell Crowe's character is named "The Spaniard”. The term "Spaniard" comes from an Old French word, which wasn't invented until the 14th century. Gladiator is set in the year 180.
In the movie, Jodie Foster’s character sets propane on fire, and then drops to the floor in order to avoid it as it’s rising upwards. In reality, propane is heavier than air, so it would sink to the floor and burn the people in the room.