The Wall

The Wall is a massive barrier of mostly ice stretching across the northern border of the Seven Kingdoms, separating it from the wild lands beyond. The Wall is one hundred leagues long (three hundred miles) and reaches over seven hundred feet at his highest point, although some foundation blocks in hilly regions, such as near Greyguard, send it nine hundred feet in the air.

History
The Wall was made to defend the realms of the First Men, and the men of the Night's Watch have reportedly defended the Wall against Others and other monsters for eight thousand years since the end of the Long Night.

According to legend, the Wall was built by Brandon the Builder with the assistance of children of the forest and giants, and it is protected with ancient spells and sorcery. Supposedly, Brandon placed foundations along heights wherever possible. Also according to legend, the Wall is vulnerable to the Horn of Joramun.

Wizards generally believe builders of the Watch used sledges to transport ice cut from frozen lakes in the haunted forest.