A crowdfunding campaign has been launched to raise money to help preserve Clawdd Offa.
The Offa's Dyke Association said that the ancient monument has been damaged by "centuries of gradual benign neglect".
A 2017 survey showed that just 8.7% of the Dyke was in a "favourable condition".
The Dyke was constructed in the late 8th Century by Offa— the Anglo-Saxon king of Mercia.
Although it is not entirely known why Clawdd Offa was originally constructed, the Dyke delineated the border between the Anglo-Saxon kingdom of Mercia and the Welsh Kingdom of Powys.
The Dyke still roughly corresponds to the present day border between Cymru and England.
Clawdd Offa is a Scheduled Monument which means that it is considered to be a significant archaeological site.
Dan Llywelyn Hall of The Offa's Dyke Association described the monument as being "hugely important to our identity of Wales"