EXPERTS have found evidence indicating that Corfe Castle was once one of the six most important in England.
One of the intriguing discoveries is thought to be a "pelican in her piety", unnoticed for centuries.
A National Trust project to restore and repair stonework has revealed elaborate Norman features suggesting that Corfe would once have equalled the White Tower, principal part of the Tower of London, in status.
One of the features discovered was an "appearance" doorway, designed for Henry I, who built the keep in the early 12th century.
Conservators have also found the remnants of elaborate carvings, showing that the castle was more highly decorated than previously thought.
One of the most curious is the shape of a bird on a pillar of the doorway to the King's Chamber from the Great Hall.
Experts have identified it as a pelican, a religious symbol found only in chapels and Royal quarters of the Norman period.
A "pelican in her piety" symbolised the sacrifice of Christ on the Cross.
Conservators also found signs that medieval builders took a few shortcuts - the masonry on some walls is far superior to that at the side or rear.
At the top of the east wall, conservators found traces of wooden scaffolding mixed into the mortar to bulk it up.
Pam White, Corfe Castle's community learning officer, said: "The masons probably got to the end of the day, couldn't be bothered to haul up yet another bucket of mortar and threw in a rotting hurdle. It's a timeless bit of bodging that reminds us that this castle might have been grand, but it was built by ordinary people."
Visitors will be able to see the results of the two-year restoration programme this summer as, after two years of closure, they can explore the keep. An exhibition is also being put on at the Castle View Visitor Centre.
Evening tours are running every Tuesday from July 1 until the end of October.