The University of Dublin is the oldest university in Ireland, dating from the 16th century, and is located in the city centre. Its sole constituent college, Trinity College (TCD), was established by Royal Charter in 1592 under Elizabeth I. It was closed to Roman Catholics until 1793, and the Catholic hierarchy then banned Roman Catholics from attending until 1970. It is situated in the city centre, on College Green, and has over 18,000 students.