Plans to build a road tunnel under Stonehenge are being scrutinised at a public inquiry.
Planners want to take the A303 under the World Heritage Site to reduce traffic congestion around the stones and improve visitor facilities
The £193m project's aim has widespread support, but campaign groups argue the proposed 2.1km (1.3 mile) tunnel is too short and will damage the site.
The inquiry, in Salisbury, Wiltshire, began on Tuesday.
Before the inquiry opened, the Campaign to Protect Rural England (CPRE) said the government's plan did not go far enough.
The group said the road would have a "major impact" on the site, with tunnel portals degrading the landscape near the ancient stones and the road and associated earthworks affecting a large area.
CPRE's head of transport policy Paul Hamblin said there was agreement the tunnel was needed.
But he added: "When building new roads we should do all that we can to ensure they are of the highest environmental standards.
"The government needs to dig deep to find what it takes to deliver a longer tunnel for this priceless world asset."
21st century noise
The National Trust is also calling on the government to accept its case for a longer tunnel.
Director Martyn Heighton said: "The public inquiry needs to consider whether the proposed tunnel is long enough to conserve and enhance the spirit of place, landscape and archaeological interest of Stonehenge."
STONEHENGE IN MODERN TIMES
1986: UNESCO declares the area a World Heritage Site
1995: Planning conference agrees on 4km bored tunnel
Government opts for short 'cut and cover' tunnel
1999: Government reveals preferred route for tunnel
2002: Government changes plans to short bored tunnel
2003: Draft orders published
17 February 2004: Public inquiry launched
He said the Trust was concerned the tunnel exits would be places on archaeological and "visually sensitive ridgelines".
A Bronze Age earthwork - which formed the ceremonial approach to the stones - would remain severed by the A303 and further areas would continue to be plagued by traffic, the Trust will argue.
"We cannot sell Stonehenge short," he added.
English Heritage - which is sponsored by the Department for Culture, Media and Sport - said it supported the Highways Agency's proposals.
It said the road scheme would "rescue" the site from the "noise and clutter of the 21st century and give it the dignified setting it deserves".
Work will start by 2005 if the scheme is approved.