In May 1998 the school of Hogwarts rose up and defended itself against Lord Voldemort and the Death Eaters. The spell was cast by Professor Minerva McGonagall, the Transfiguration Professor at the time. The spell “Piertotum Locomotor” is more of an animation charm (locomotor) that works on items make primarily of stone (pierre) but also metal and animates suits of armour, statues, and humanoid items. The Professor is known to have interjected the spell with:

“Man the boundaries, protect us, do your duty to our school!”

The transfiguration meant that there were fewer casualties and more defences battling that night.