The Frateris Templar were the military order of the Ecclesiarchy for several centuries.
The Frateris Templar were founded soon after the Ecclesiarchy moved away from Terra and to the planet Ophelia VII in order to escape Administratum domination. With the previous restraints removed, the Ecclesiarchy began to grow in power, forming its own interstellar fleet and armies, which became known as the Frateris Templar. The forces numbered many commercial and war ships, and dozens of armies, each possessing the strength of an Imperial Guard regiment.
The Frateris Templar was an all male military order and operated effectively as the private army of the Ecclesiarchy. At times it was used to crush revolts against Ecclesiarchy power.
The Age of Apostasy
Three hundred years after their founding the Ecclesiarchy moved back to Terra and the insane Goge Vandire seized the Ecclesiarchy as his own. When a man known as Sebastian Thor led the Confederation of Light in revolt against Vandire's tyranny, Vandire sent Frateris Templar to destroy him and the confederation, along with every living creature on the planet. However en-route to the planet the Templar fleet was engulfed in a warp storm and destroyed, the storm later came to be known as the Storm of the Emperor's Wrath.
After Vandire's defeat the Frateris Templar was fully disbanded and the Ecclesiarchy was barred from ever holding any men under arms. Their role was taken over by the Adepta Sororitas.