Heritage campaigners fear cabling for a new windfarm could wreck an important archaeological site.
The cross dyke at Tottington Mount, near Upper Beeding, dates back as far as 2000BC.
Energy giant E.ON wants to dig under the Bronze Age monument for cabling to connect the proposed offshore Rampion windfarm to the National Grid.
The cable will go through the South Downs National Park to connect the 195 turbines off the Sussex coast between Brighton and Newhaven to an electricity connection at Bolney.
E.ON said the cable could not avoid the monument due to steep slopes on either side of the site.
But conservationists are demanding the cable be rerouted away from the protected monument altogether.
Steve Ankers, a planning officer for the South Downs Society, said: “If the cable was situated further east it would avoid the national park altogether.
“The cross dyke is one of the most sensitive parts of the route and the plans do not recognise the archaeological importance of the whole national park area.”
Chris Todd, from Brighton and Hove Friends of the Earth, said he was “sceptical” of the need for the cable route to go through the ancient monument.
He said: “E.ON needs to appreciate the need to value heritage and protect it where possible.
“It seems odd that it requires an 8.7- mile cable route through the national park at a point where it is only two to three miles wide.”
Mr Todd said a 12-week public consultation, which concluded last Sunday, was “unsatisfactory” as no Environmental Impact Assessment was published.
E.ON is now in discussions with English Heritage over the Tottington Mount site.
The site is a Scheduled Ancient Monument which requires a recommendation by the conservation body to the government before work can be carried out.
English Heritage experts believe the site contains buried archaeological remains.
A spokesman said: “Very few have survived to the present day and hence all well-preserved examples are considered to be of national importance.”
Victoria Blake, from E.ON, said: “We are doing everything we can to ensure the cable crosses in an acceptable way and has minimum impact on the area.
“The disturbance should be as little as possible.”