Marking one of the medieval viewpoints and one of the entrances to the city, the Santiago Tower still retains its medieval appearance, which contrasts with the rocaille decoration that covers the north facade. It is divided into two registers: the upper one is marked by the clock and the stone bell tower and the lower one by the Oratory of Our Lady of the Tower, added in the 18th century.

The chapel was designed by André Soares and was built in thanksgiving to the Virgin for protecting the college during the great earthquake of 1755, which caused great destruction throughout the country.