Some engineers recently weighed in on whether or not the massive ice Wall that's a central feature of the landscape in George R.R. Martin's A Song of Ice and Fire fantasy series could actually be built. The wall was built with magical assistance and keeps the mysterious creatures of the lands Beyond the Wall from invading the human-populated lands of Westeros.
The wall is supposed to be 700 feet high and nearly 300 miles long, but an engineer at Dartmouth College said that a wall of such height would not be stable. The weight of the ice at the top would press down on the ice at the bottom, causing it to bulge and deform.
The problem is that ice is a solid under certain temperature and pressure conditions. At sea level air pressure, water freezes at 32 degrees Fahrenheit. But if the pressure is increased, then the temperature needed to freeze the water is lower and the solid ice will regain some of its fluidity. Weight can duplicate the effects of greater air pressure; if you take a block of ice and lay a string on top of it that has weights tied to either end, the string will gradually melt the ice directly underneath it until the weights reach the ground, relieving the pressure the string puts on the ice. Of course, the weights have to be heavy enough and the temperature warm enough to make this happen. In other words, the Wall is too large to be built the way it is described. It would collapse under its own weight.
Now there's a metaphor for this particular series that works!