Glaciers can be very high/thick (miles).
However, if the thickness exceeds 50 m, the ice starts to behave more like a liquid or something due to the pressure. Not sure what would happen, but my guess is a free standing (relatively thin) wall of ice would either slide away or more likely the lower layers get pushed out more and more while the overall Wall gets shorter and shorter. Resulting in a pile of ice at some point.
(but anyway it's magic ice considering no one could have built it by normal means, unless you stack blocks of ice for a long time I guess)