Which northern european humanist wrote a book that imagined a peaceful society without private property?

You are probably talking about the book Utopia written by Sir Thomas More, which is considered a saint in the Roman Catholic Church and Anglican Communion. Thomas More was an English lawyer and a noted Renaissance humanist that served the court of Henry VIII of England. In the Utopia, More described a fictional island society with ideal religious, social, and political customs. The society is perfectly orderly, with very simple laws, and social gatherings in public view so participants will behave. Communal ownership supplants private ownership, men and women receive good education, and there is good degree of religious toleration. The Utopia is More’s most famous work.

they made rome the dominant power in the mediterranean.