The Stonewall Pact
The Order of the Aegis
The Council of the Bulwark
The Guardian Order
The Shieldbearer Quorum
Holy Order of the Barricade
The United Brotherhood of the Rampart
The Ziggurat Priests
Bishops of the Bastion


Mix and match pieces of those until something rolls off the tongue.

I would also use lots of these words (Aegis, Buttress, Bulwark, Bastion) as ranks. Rather than spikey things that suggest spears, rather than shields.