The Royal Commission on the Ancient and Historical Monuments of Scotland has defined a Dun as 'a comparatively small defensive enclosure with a disproportionately thick dry-stone wall enclosing an area that rarely exceeds 375 sq m (4000 sq ft)'.

The earliest duns are thought to date to the 7th or 6th centuries BCE, but the majority were probably in use from the 1st to the 3rd centuries CE.  They were built as defensive settlements, the best preserved on Mull being Dun Aisgain, near Burg, south-west Mull, although there are a great many others scattered along the coastline.  They are usually situated on small islands, the summits of low hills and knolls, rocky crags, and at the end of coastal and inland promontories, and are distinguished from forts by their relatively small size and the disproportionate thickness of their walls.  It is assumed that they were designed to provide defence for extended family units, whereas forts were intended to provide refuge for whole local communities.  Most duns are oval in plan, but they can be almost circular or irregular in shape where they have been adapted to the shapes of natural crags.

Below is an alphabetical list of Mull's duns.  Where the name is highlighted, more detailed information is available, sometimes including images.  Click to go to the link.  Please check back for further information as the Society has an ongoing updating programme.

Allt Cill Chriosd, Mornish
An Caisteal, Bunessan
An Dun, Killunaig/Torrans, Loch Scridain
An Sean Dun, Glengorm

Cnoc na Sroine, Glenaros, Salen
Cruach Sleibhe, Calgary

Dun a Chiabhaig, Uisken
Dun a Geard, Kilvickeon,  Assapol
Dun Aisgain, Burg, Loch Tuath
Dun Aoidhean, Isle of Erraid
Dun Auladh, Druimghigha,Croig
Dun Ban, Tostarie
Dun Bhuirg, Burg, Loch Scridain
Dun Calgary
Dun Choinichean, Kilbrennan, Loch Tuath
Dun Earba, Garmony
Dun Haunn, Treshnish
Dun Mhadaidh, Langamull
Dun nan Gall, Croig
Dun Scobuill, Tiroran, Loch Scridain
Dun Urgadul, Tobermory
Dunan Mor, Loch Buie
Eilean na h-Ordaig, Killiemore, Loch Scridain
Kellan Wood, Loch na Keal
Port Langamull
Port na Callich, Mornish
Scallastle Bay, Alterich
Sean Dun, Kinloch, Loch Scridain
Tigh an Duine, Gometra
Torr a Chaisteil, Ardfenaig
Torr nam Fiann, Killichronan, Loch na Keal