The Magic Purification Spell was a ritual used for the purpose of purging the world of magic safe the one practiced by the Travelers 2,000 years ago which they deemed 'pure'. It was performed by the Travelers using the combined blood of the last pair of Doppelgängers, Stefan Salvatore and Elena Gilbert.
The spell was a plan conceived by Markos with the intention of breaking the curse cast upon them 2,000 years prior by a coven of witches. It began in the Town Square of Mystic Falls and its effects radiated outward from there until the spell was ultimately halted by the death of one of its doppelgänger, Stefan, at Julian's hands. As a result, this series of events made Mystic Falls a magic-free zone, whereby any object or supernatural being created by magic were quickly depowered upon crossing its borders.
It was eventually reversed when Malachai Parker, a Siphoner, managed to absorb the power of the spell thereby unraveling the Magic Purification Spell and negating its effects on the supernatural community of the town.