If you've been watching the fifth season of Game of Thrones, no doubt you've been a little alarmed by the actions of Lancel Lannister and the other members of the Faith Militant. The long-banned military arm of the Faith of the Seven was reinstated by Cersei in "The Sons of the Harpy," and the order of religious warriors wasted little time in dispensing "justice" to those they viewed as sinners.

Among those sinners was Loras Tyrell, the brother of Queen Margaery. Cersei bringing back the Faith Militant is all part of her plan to get at Margaery and gain more control over King's Landing by hand-picking the new High Septon, but she might not understand the can of worms she just opened, as we will see in future episodes.

To understand just how serious a threat the Faith Militant at one time posed to the Iron Throne and might pose once again, you have to dive into the history of Westeros, in the early years of the Targaryen dynasty. Most of the following information is taken not from Martin's novels but from his Game of Thrones history book The World of Ice and Fire.

The Faith Militant is actually comprised of two groups: The Warrior's Sons and the Poor Fellows. The Warrior's Sons are the elite warriors of the Faith, reporting directly to the High Septon and following his will. These warriors were often knights of various sorts, and occasionally included men of prestigious noble houses. The Poor Fellows is a far less elite group, made up of common men and women who often wander the land and help escort the faithful from sept to sept.

Together, however, these two groups form a potent fighting force. Four decades after Aegon the Conqueror established his Targaryen dynasty in Westeros, during the reign of Maegor the first, the Faith Militant proved to be a major threat to the Iron Throne.

The Faith Militant, led by the High Septon of the time, staunchly opposed Maegor's rule after he bypassed his brother's son to take the throne. The leader of the Warrior's Sons at the time challenged Maegor to trial by seven over the matter, in which the warrior Ser Damon Morrigen and six other men battled against Maegor and his six champions. When the dust settled, 13 men died. Maegor was the sole survivor but fell into a coma for 27 days.

When he woke up he wasn't happy. He flew atop his dragon and roasted hundreds of the Warrior's Sons alive as they prayed, positioning archers around the Sept of Remembrance to eliminate any survivors.

That was just the beginning of Maegor's war against the Faith Militant. And it truly was a war. Battles with thousands of men on both sides swept across the seven kingdoms, as rebel lords opposed to Maegor joined forces with the Poor Fellows and Warrior's Sons. Despite a new High Septon taking charge of the Faith Militant and urging them to lay down their arms, the rebellious group refused.