The southern sea gate (the Porta Aenea) was simpler in shape and dimensions than the other three, and it is thought that it was originally intended either as the emperor's private access to the sea, or as a service entrance for supplies.
A porta do mar do sur (a Porta Aenea) era máis simple en forma e dimensións que as outras tres, e crese que deseñouse orixinalmente como o acceso privado do emperador ao mar ou como entrada de servizo para o abastecemento.