Offa's Dyke damage done 'in ignorance'

But experts have warned it highlighted a gap in the current law designed to protect historic monuments.

The damage was done on land at Chirk, on the Shropshire/Wales border, bought by two travellers.

Correspondence by North Wales Police and officials from the Welsh historic monuments body CADW has now been released under the Freedom of Information Act.

In it CADW said the new owners claimed the land had been advertised as ideal for stables and a paddock and neither the seller nor their solicitor had informed them of the protected status of the site.

Wrexham CID told CADW that no further action would be taken "due to both parties' solicitors not identifying Offa's Dyke" and because officers couldn't prove whoever was responsible for the damage knew the site was part of the 1,200-year-old earthwork.

But CADW said the decision not to prosecute highlighted "a failing in current legislation under which the monument is protected."

A criminal offence is only committed when someone causes damage knowing it was a protected monument and with intent to destroy or damage. "It is therefore a defence to demonstrate ignorance of the protected status," an official explained in the FOI documents.

The trail, popular with ramblers, runs for 177 miles from Prestatyn in North Wales to near Chepstow on the mouth of the River Severn.

Historians have always linked the dyke with King Offa, the Mercian (English) king who ruled in the eighth century, and have thought it was there as a warning to the Welsh, or as a defensive wall. It is up to eight feet high and 65 feet wide and previous estimates were that its construction was between 757 and 796AD.

According to legend, there were violent repercussions for those of either nationality who strayed to the "wrong" side.

Recent research by the Clwyd-Powys Archaeological Trust has suggested that at least part was built up to 200 years earlier than thought.