40Conwell, failing to discover a passage into Cairn D, concluded that the monument must be a cenotaph, also known as a "blind cairn," a monument with no burial chamber, perhaps used as a memorial. However as Martin Byrne points out, "It is highly unlikely that the Loughcrew builders would put so much effort into such a massive cairn and leave it blind." (Byrne, Martin. "Cairn D at Loughcrew." The Sacred Island. Web. 24 Nov. 2013. <http://www.carrowkeel.com/sites/loughcrew/cairnd.html>.)