Why was travel difficult in ancient greek times?

What project establish leonardo da vincis reputation as a creative and talented engineer

In ohio in 1872, the cleveland massacre was a)a violent labor dispute at standard oil refineries in cleveland. b)a takeover by standard oil of the refineries in cleveland. c)an attempt to stop standard oil from becoming a monopoly. d)a failed attempt by standard oil to take over other refineries.

What were some effects in world war 1 in europe ? ( and only in europe)