Dunnideer | is it a fort, a tower house, or a castle | and when was it built?

Dunnideer, is it a fort, a tower house or a castle? And when was it built?
Sitting on top of Dunnideer Hill, near Insch in Aberdeenshire, is the ruinous remains of a former important stronghold. Dunnideer castle is purported to be the earliest recorded town house on mainland Scotland. The first documented mention of a Castle on Dunnideer Hill was in 1260AD, but when was it built?
Dunnideer Hill lies on the outskirts of Insch in Aberdeenshire and the iconic tower of the former castle that sits on its brow, can be seen for miles.
Access to the castle is via the short but steep slopes of Dunnideer Hill. There is a clearly marked and well trodden path up to the summit - watch the rabbit holes; there’s plenty of them! - and a small off-road layby with space for around four cars at the bottom of the hill.
As you near the top of the hill, you start to see some changes in the landscape; the ground becomes harder and you start to see vitrified stone. You also see undulations, indicating a circular shape. Was this castle an earlier fort, perhaps?
It’s interesting to note that the marvel of Pictish art which is the Picardy stone, sits in direct line of sight to the castle. Could it be related to the castle in some way? It is, indeed believed to be to the marker of a burial chamber relating directly to an earlier fort which was strategically located on this hill. That fort is believed to have been built in around 880AD by the great Pictish nobleman Girich, King of the Picts, also known as Gregory the Great of Scotland.
There is a suggestion that a castle was built here in 1178AD by David, the Earl of Huntingdon and Garioch. But the first documented reference to a castle here doesn’t appear until 1260AD, when Josceline de Balliol, the then Lord of Dunnideer, granted the Abbey of Lindores access to the land on the condition that the Abbot should pay him and his heirs a pair of white kid gloves every Whitsunday. This reference to there being a castle here in 1178 possibly makes Dunnideer Castle the earliest surviving tower house in Scotland.
The tower is built from vitrified stone which it’s thought came from the original Pictish fort. Vitrified stone is stone which has a glassy appearance that comes from it having been exposed to extremely high temperatures, i.e. fires. In 2008, two carbon samples were taken from the exposed stone and radiocarbon dating indicated that the vitrification took place sometime between 550 and 250BC, during the Iron Age when it’s known that the first brochs, stone towers with outlying concentric circles, were built in Scotland.
There are some other important historical characters connected to Dunnideer too. Besides the already mentioned King Girich, Jocelin de Balliol and Earl David, family members and heirs of these people include, amongst others, King Malcolm, King William, and Robert the Bruce.
To answer the question of when this castle was built, we need look at the known history of the buildings that have occupied this site. The ruinous tower that remains today was probably built in the 1100s, but the stone that it’s built from came from a Pictish fort which dates back to around 880AD. However, there is irrefutable evidence that there was an even earlier fort here, built sometime during the early Iron Age, in about 500-250BC - before the Romans came to town! It’s pretty old!
And to think that we were walking a route that Iron Age people, Pictish Kings and even Robert the Bruce might have walked, well that’s pretty amazing too!