Estate parklands in Carmarthenshire famed for historic landscapes, woodland and rare species have been designated a National Nature Reserve (NNR).
Some of the oaks on the estate are around 700 years old
This means that more resources will be available to manage conservation work at the Dinefwr Estate, near Llandeilo.
The estate's lichen and insect populations are described as exceptional with more than 160 lichen and 400 beetle species recorded.
It is the first time any Welsh parkland has been given the NNR designation.
The parklands, which are already a Site of Special Scientific Interest (SSSI), are also well known for their ancient trees.
Some of the oaks are about 700 years old and many are left to die slowly as the dead wood is a rich habitat for many insects.
Iwan Huws from the National Trust in Wales, which co-runs the Dinefwr Estate with the Wildlife Trust, said the large numbers of these old trees reflected that they had probably been managed for at least 500 years.
The recently expanded herd of white park cattle also linked the estate back to the native Welsh rulers of medieval times, he said.
They were once used as payments in 10th Century Wales to the Welsh princes and are now used to help manage the parkland's wildlife interests.
The history of the estate stretches back to the Iron Age. A recent survey of the land found an Iron Age promontory fort and two overlying Roman forts.
Dinefwr's castle was once the residence and power base of the princes of the ancient Kingdom of Deheubarth from the 10th Century.
Conservation projects are already underway to restore the estate's 18th Century-designed landscape to its former glory.
These have been funded by the European Union's Objective One programme, the Heritage Lottery Fund and a private legacy left to the National Trust.
Cattle like these were once used as payments to Welsh princes
Traditional styles are replacing modern fencing, historic walls are being repaired and plantations of poplars and conifers are being replaced by thousands of young oak trees.
Major improvements to Newton House, the centrepiece of the landscape design, have been undertaken, as well as the creation of new paths and information for visitors.
John Lloyd Jones, chairman of the Countryside Council for Wales, which designates the NNR statuses, said the Dinefwr Estate's new status reflected its "outstanding" natural features.
"A visit to Dinefwr today is far more than an opportunity to enjoy nature at its best - thanks to the restoration work, it is a living testimony to one aspect of Wales's rich cultural and historical past," he said.
The NNR is the highest designation awarded to areas of exceptional wildlife and conservation importance.