Siege Perilous (comics) - First

First

The first Siege Perilous, which appeared in Captain Britain #1 and 2 (1976), was a circle of standing stones which transformed Brian Braddock into Captain Britain.

In the 2008 "Secret Invasion" storyline, Earth was attacked by a Skrull armada and a wave of empowered Super Skrulls. The Skrulls had infiltrated the ranks of the British government, though they were exposed by John, a Skrull turncoat loyal to MI:13 and who had taken the form of John Lennon. The Skrulls' target was the Siege Perilous. Captain Britain and his team head there to defend it.