1Westropp, T.J. "A Study of the Fort of Dun Aengusa in Inishmore, Aran Isles, Galway Bay: Its Plan, Growth, and Records." Proceedings of the Royal Irish Academy Section C: Archaeology, Celtic Studies, History, Linguistics, Literature 28 (1910): 32.

2Westropp 34.
He writes, "An unrestored fort is its own record; but, to one who recalls the weird chaos of ruin-heaps in 1878, and contrasts it with the neat, level-topped enclosures left by the restorers six years later, the old descriptions, no matter how rude, assume a great importance, and should be laid before one's readers." Westropp continues on p. 45: "The unnecessary rebuilding and levelling up of parts of the walls and the "tidy" and new appearance thereby produced, show how desirable it was that the work should have been constantly under the supervision and direction of an antiquary who had studied our ring-walls carefully. Left to non-antiquaries and the natives, the work was of course done unsympathetically, like repairing a fence…"

3Dalton, John P. "Who Built Dun Aengus? (Continued)." Journal of the Galway Archaeological and Historical Society 14.3/4 (1929): 110.
The author suggests that King Aengus made a living as a pirate: "…unless they still resorted periodically to sea-raiding and smuggling. Aenghus could have kept up but the very poorest semblance of a royal court at Dun Aengus."
Another possibility, reported by Westropp (quoting Edward Ledwich, 1790) is that Dun Aengusa was named much later, after an entirely different Aenghus, one who was King of Cashel, c. 460 CE.

4"Lebor Gabala Pt. 3." AKA Mary Jones. Web. 04 June 2011. <http://www.maryjones.us/ctexts/lebor3.html>.
The full text may be read at this web site.

5Westropp 12.

6Norman, Edward. The Early Development of Irish Society the Evidence of Aerial Photography. Cambridge: University, 1969. 81-82.
Also: Long, Harry, and Etienne Rynne. "Dún Aonghasa." Journal of the Galway Archaeological and Historical Society 44 (1992): 21.

7Excavations.ie. Searchable Database of Irish Excavation Reports. Web. 05 June 2011.1992 Report. 1993 Report. 1994 Report. 1995 Report.

8Long 11.
The authors on p. 17 suggest that Dun Aengus and its chevaux-de-frise play an important role in discussions of the origin of Celtic groups in Ireland. "The question of when and by what routes Celtic-speaking peoples first arrived in Ireland is fraught with controversy and doubt. The stone chevaux-de frise at Dún Aonghasa is seen as evidence of the influx from Iberia of people speaking Q-Celtic in the wake of the Roman conquest of 133 B.C.33. Some philologists, however, associate the Fir Bolg of Ireland with the Belgae of Belgium and France, who may have occupied sites where, earlier, wooded chevaux-de-frise have been found. Dún Aonghasa is thus at the centre of a debate in which the chevaux-de-frise is used to argue two different opinions."
One of the other three examples of chevaux-de-frise is also on the island of Inishmore, at Dun Dúbhchathair, the Black Fort. There is a virtual-reality view of this fort (from a distance) on the Dun Aengus page.

9Westropp :21-22.

10"Dun Aengus." University of Notre Dame. Web. 05 June 2011. <http://www.nd.edu/~ikuijt/Ireland/Sites/acastela/site/index.html>.

11Westropp 34.
In addition to Westropp's work in 1909, the most significant of the other investigators were: Roderick O'Flaherty (1684-6) "Ogygia"; Edward Ledwich (1797). "He gives a delusive view...regards the fort as a mandra or monastic enclosure"; John O'Flaherty (1824); George Petrie (1821 and 1857); John O'Donovan (1839); Samuel Ferguson (1853); John Windele (ante 1854); Lady Ferguson (1867). "The Irish before the Conquest"; and Lord Dunraven (ante 1875). He took photographs before the restoration.

12Petrie, George, and D. J. S. O'Malley. "Aspects of George Petrie. V. An Essay on Military Architecture in Ireland Previous to the English Invasion." Proceedings of the Royal Irish Academy Section C: Archaeology, Celtic Studies, History, Linguistics, Literature 72 (Read, 1834. Published, 1972): 247-48, 266-68.

13O'Flaherty, John T. "A Sketch of the History and Antiquities of the Southern Islands of Aran, Lying off the West Coast of Ireland; with Observations on the Religion of the Celtic Nations, Pagan Monuments of the Early Irish, Druidic Rites, &c." The Transactions of the Royal Irish Academy 14 (1825): 97-98.

14Evans-Wentz, W. Y. The Fairy-faith in Celtic Countries. London: H. Frowde, 1911. 416.
As Petrie noted perspicaciously 77 years earlier: "The Antiquities of Ireland have already attracted the attention of several learned men, but the antiquarian knowledge of those persons was confined to literature—they had no general or accurate acquaintance with the ancient remains of our own and other countries. It was therefore but natural that their labors whether guided by a Spirit of rational enquiry, or led on by visionary national predilection, should have almost equally tended to darken rather than elucidate the subjects of their investigation."

15Westropp 1-2.
He writes, "Of all the early forts of Ireland we may say that only one has appealed to the imagination, and even to the affection, of the nation, as a building, and become, with most antiquaries, the type and symbol of the countless similar structures, all subordinate to it in interest. At Emania and Tara it is the sentiment and tradition, not the remains, that so appeal ; but at Dun Aengusa the site and the building affect even the coolest mind as no place of mythic or historic association could do."

16Wakeman, William F. "Aran – Pagan and Christian. Part I." Duffy's Hibernian Magazine 1. January-June (1862): 470.
This article may be read in its entirety here.

17Westropp 36.

18Gannon, J.B. "The Unveiled Aran." The Irish Monthly 73.870 (1945): 519-22.

19Grover-Rogoff, Jay. "Dun Aengus." The Hudson Review 38.1 (1985): 83.