Italian to English Other History summons

"Chi veniva da XXX o dalla Marina, percorrendo le antiche strade, passava attraverso una prima porta, il ponte levatoio, l’avamporta e, dopo un ultimo tratto in salita, trovava la porta di accesso alla cittàThe entire sentence is "porta di accesso alla città".

This is a description of a town's medieval fortifications. There appear to be three successive gates. There is a first gate, then the avamporta, which presumably is attached to the drawbridge but is, nonetheless, confusing as it is not the first gate. All of this is followed by the gates which actually gives access to the town! Any suggestions for avanporta?