Ravens have roamed the courtyards of England’s Tower of London for centuries. But the six who constitute the tower’s current flock have now—like Anne Boleyn and Sir Walter Raleigh—been imprisoned within its walls. Concerned that the birds might succumb to avian flu—now on the wing throughout Europe—Derrick Coyle, the tower’s raven master, built cages inside the 11th-century stronghold and moved the birds into them this past February. Legend has it that if the ravens, whose wings are clipped, ever leave the tower, the fortress and the kingdom will fall. “We believe it was the safest thing to do,” says Coyle.