(Below) This hand drawn map c. 1209 AD below, which has west at the top, shows the O'Callahans near Cork, Ireland. (The highlighting and circle I added.) It can be viewed online in its full size at this Dublin City University website
(Below) The Irish Saga about the first Callahan, who lived in the tenth century, was written in the twelfth century. A fifteenth century manuscript copy was found walled up in Lismore Castle in a book called "The Book of Lismore." The Callahan Saga is one section in the Book of Lismore, which has many different works bound into it. The Book of Lismore was first put on display by University College Cork in 2011 and this 2011 You Tube video is about that. It shows what the manuscript looks like.
(Below) Patrick Gleeson: Published on Dec 14, 2014 on You Tube
Patrick Gleeson presents 'Gathering the nations of early medieval Ireland: debating provincial kingship, royal government
Patrick Gleeson presents 'Gathering the nations of early medieval Ireland: debating provincial kingship, royal government and ceremony in the post-Roman West' at the Royal Scone Conference.
(Below) Dr. Patrick Gleeson – ‘Peoples, Kings and Kingdoms, Medieval Tipperary’
"Published Dec 21, 2016 on You Tube
Whilst Cashel is world famous as a former royal seat in Tipperary, there were many other seats of power and kingship dotted around the landscape of the county. In the December lecture from the Tipperary People and Places Series, Dr Patrick Gleeson, formerly of Nenagh uses the historical and archaeological evidence of these sites to illuminate local politics and society and indeed the wider place of Tipperary in medieval Ireland."
The Callahan Genealogy and History Facebook page.