The third and final phase of Iron Age Llanmelin began around 50BC when the entrance was remodelled and strengthened.
Dechreuodd trydydd cam — a cham olaf — y gwaith adeiladu ym Mryngaer Oes Haearn Llanmelin tua 50CC pan gafodd y fynedfa ei hailfodelu a'i hatgyfnerthu.