The site of Cú Chulainn’s supposed settlement at Dún Dealgan (which actually means ‘the Dún of Dalga’) was, in far more recent times, anglicized to Dundalk. When the town opened its first museum in 1901, therefore, it’s no surprise that they harkened back to the town’s imagined history rather than its real history – which involved colonisation, land grabbing, subjugation, and was a lot less appealing – to celebrate its opening.
That opening was marked with a huge outdoor pageant with numerous people dressed up in authentic fantasy costumes of the period. To celebrate the occasion four postcards were also produced.
Outdoor pageants of this type were very popular at the time but, obviously, come 1916, people had a lot more on their mind and they fell out of fashion.
Interestingly enough, go to any ‘mythology’-related event in Ireland and it seems to have become more popular again.