Spell of Humility
From GargWiki
It seems the spell has specific limits however. If a gargoyle is holding a living creature, that creature will not turn to stone with them. Even certain items will not turn to stone if (from the gargoyle's point of view) the item is not their property. This explains why Hudson's sword sometimes does and sometimes does not turn to stone (Hudson comandeered the sword from a Viking in 994).
Tidbits
Behind the scenes, the spell was a convenient plot device used by Greg Weisman to explain why an otherwise natural process would have such an unusual and unnatural side effect. Weisman has joked that the Roman Magus "must have had the backing of ALL of Rome's Standard's and Practice's Executives". [1]
Rumor has it that Brooklyn may be in Caesar Augustus' court as the spell is cast on his TimeDancer journey.
