Links with further information about the Irminsul:
http://englishnews.org/news-central/germanic-symbols/irminsul.html
https://en.wikipedia.org/wiki/Irminsul
http://www.odinic-rite.org/main/the-irminsul-and-the-externsteine-from-yggdrasil-to-the-irminsul/
http://honortheroots.com/irminsul-heathen-symbol-of-pagans/