If you traveled back in time to the days of ancient Rome, how would you show that you came from the future?

It is pathetic to think about, but there is very little I could do. I might be able to convince people by foretelling of certain events. I could introduce decimal numbers, but could not calculate faster than someone using an abacus. I could show how to use algebra, which some people might find amusing but not of much use. I might be able to construct a crude battery, but would not be able to do much with it. I could show how to use perspective to draw a cube.

On the other hand, people might be surprised by my ignorance. I don’t know how to slaughter an animal, make cloth or clothing, ride a horse or drive a chariot and I don’t recognize most constellations.