Tonn Tinne

The other prominent "Fire Hill" visible from Uisneach in Tipperary is Tonn Tinne. Now Tonn Tinne also has many other claims to fame other than this.
During the middle ages, chroniclers when recording the story of the origins of the Irish are thought to have grafted a Biblical origin onto the story linking the first Irish people to Old Testament stories. The story goes that the first Irishman was Fintan mac Bochra who came with his 5 wives to Ireland before the Biblical Flood. One of Fintan's wives was Cessair the grand-daughter of Noah.
What has this got to do with Tonn Tinne near Portroe I hear you ask? Well after the flood, Fintan was the only survivor as he managed to hide in a cave on Tonn Tinne known as Fintans Grave.
Next Wikipedia says "He then turned into an eagle and then a hawk then back to human form. He lived for 5500 years after the Deluge, becoming an advisor to the kings of Ireland. In this capacity he gave advice to the Fir Bolg king Eochaid mac Eirc when the Tuatha Dé Danann invaded, and fought in the first Battle of Magh Tuiredh.
He survived into the time of Fionn mac Cumhail, becoming the repository of all knowledge of Ireland and all history along with a magical hawk who was born at the same time as him. They meet at the end of their lives and recount their stories to each other. They decide to leave the mortal realm together sometime in the 5th century, after Ireland was converted to Christianity."
https://en.wikipedia.org/wiki/Fintan_mac_B%C3%B3chra
Now why the chroniclers picked Tonn Tinne as the location of Fintan's Grave is not known. However I would imagine they may have borrowed from some other story or myth linking a flood at this location.
On the sloop of Tonn Tinne is of course the "Graves of the Leinstermen" which is recorded as a megalithic structure. I've written before that it may have been a Neolithic court-tomb.
http://thetipperaryantiquarian.blogspot.ie/…/graves-of-lein…
There is also a bronze age hillfort less than 500m away at Laghtea and of course the Capstone of the King of Leinster is another monument in the vicinity which is not fully understood.
http://thetipperaryantiquarian.blogspot.ie/…/the-capstone-o…
So it could be that the Graves of the Leinstermen are the remains of Fintan's Grave. It could also be that there is another unknown monument waiting to be discovered under the peat on the summit or slopes of Tonn Tinne or even an actual Cave. However I did a brief check of the underlying geology of the area and it appears that it isn't conductive to the formation of Caves.
As we mentioned before the meaning of Tonn Tinne is either "Wave of Fire" or "Grave of a person". The 2nd could link it into the story of Fintan.

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Other folklore relating to Tonn Tinne

From Ballina/Boher: Our History and Traditions" by Kevin M. Griffin and Kevin A. Griffin. Thanks to Joanne Hinz for passing these on to me.

pg 39 "Another extraordinary story about the Graves of the Leinstermen comes from the Book of Leinster, and is also mentioned in other ancient sources, which call the site 'Firt Fintan.' According to the ancient writers, Fintan was said to have slept here and he slept so soundly and so well that the Great Flood of the Bible failed to wake him or drown him! Later he used to wake up at intervals telling the history of the past, and collecting that of later times. Because of this he was considered to be the main transmitter of the remote story or ancient history of Ireland." 

This comes from a footnote in Westropps account in the Proceedings of the Royal Irish Academy. Section C: Archaeology, Celtic Studies,
History, Linguistics, Literature, Vol. 29 (1911/1912), pp. 186-212 - see page 211.

pg 19 "Tountinna; Tone Tinne: "Wave of fire or Hill of the wave."  "This is Tul Tuine, Hill of the Wave--the place where Fintan was buried... In the N.E. end of parish. It chiefly consists of mountain. On the N.E. are two small lakes and a trig. Station, 1500 feet above low water at the sea. Bounded on the N. by the parish of Youghal Arra." 

The nearby townland of Townlough Upper & Lower splits the townland which the Capstone of the King of Leinster is in from the townland of the Graves of the Leinstermen. Townlough itself translates as Tuaim Locha or basically burial place by the lake or perhaps burial mound by the lake but there is no record of any such monument in that townland