The faculty and nation system of the University of Paris (along with that of the University of Bologna) became the model for all later medieval universities. Under the governance of the Church, students wore robes and shaved the tops of their heads in tonsure, to signify they were under the protection of the church. Students followed the rules and laws of the Church and were not subject to the king's laws or courts. This presented problems for the city of Paris, as students ran wild, and its official had to appeal to Church courts for justice. Students were often very young, entering the school at 13 or 14 years of age and staying for six to 12 years.