The castle was built by the Earl of Chester, Hugh D'Avranches.
A little-known castle dating from 1088 has been rescued from further deterioration on Anglesey.
Castell Aberlleiniog near Llangoed, is a scheduled ancient monument and is the island's only example of a 'motte and bailey' castle.
It is owned by Anglesey enterprise agency Menter Mon.
The conservation work was paid for with a grant of £317,500 from the Heritage Lottery Fund and £161,000 from Cadw, the historic moumuments' agency.
'Motte and bailey' castles were built on a mound (the motte), with a bailey or enclosed courtyard below.
The restoration work was carried out by a specialist team of local archaeologists and heritage construction contractors and stonemasons.
It involved stabilising the castle 'motte' to provide a secure foundation, before carefully dismantling the towers and the walls, by hand, and meticulously re-building them stone by stone.
Cadw inspector Mike Yates said the work had been done "just in time".
Pottery and tobacco pipe stems
Button made from coppery alloy
Lead musket ball and lead strips
Halfpenny dating from 1701
"For over 20 years I have observed the progressive deterioration of this site as the mound suffered from erosion by livestock, and the masonry became increasingly unstable and overgrown by vegetation," he said.
"It is therefore of huge personal satisfaction to see the monument conserved before too much was lost," he added.
Jennifer Stewart, head of Heritage Lottery Fund (HLF) Wales said castles were a key element of Wales' heritage and helped make the place unique.
She said that saving the castle had ensured the archaeological resources at Aberlleiniog which "spans over a millennium", and information about Anglo-Norman structures, had been secured for future generations.
Local people were being encouraged to get involved as volunteers to help look after the site, she added.
A before and after picture of the west tower
Archaeologists working alongside the conservators also found interesting items.
Project Archaeologist Tim Morgan said: "Items found range in date from about 1640 to perhaps the late 18th Century, focused especially on the Civil War defence of Aberlleiniog, and the subsequent conversion of the 'motte' into a folly soon after 1700."
Despite the small number of finds, they showed a "remarkable variety of forms, at once illustrating the military and domestic occupation of the castle", he added.
The castle was built in the 11th Century for Hugh d'Avranches, the 1st Earl of Chester, marking the Normans furthest reach into north Wales.
It was replaced with a stone structure during the Civil War in the 17th Century.
The public can now visit the site and Menter Mon has footpaths information available.