Sounds like a great chance to show him the 'cross' reference in the reasoning book. it references the Imperial Bible Dictionary dishonestly. Here is a link to the real page it claims to quote.
http://archive.org/stream/theimperialbible01unknuoft#page/376/mode/1up
With the entire roman rule being incredibly well documented, it's amazing they've gotten away with saying thT Romans didn't kill people on crosses for this long.
Good luck