The magewall was the magical shield that surrounded the Valley of Tamingazin on Dominaria. It was devised by the Institute of Arcane Study to protect the valley from intruders. Whoever tried to cross the barrier could do so, but was slowed down by a factor of at least 25 on the border. This effect also increased with each person going through, effectively shutting out foreign armies.
The magewall was a self-sustaining enchantment, but could be controlled using an artifact called the Magewall Hub.