Ley Line

While the lower tiered rituals will be usable at anytime the higher tier rituals will require "Power" to be wielded. Ley lines run through the land linking Places of Power that radiate energy for your spells. Casting in a suitable Place of Power will let you cast the most powerful of rituals, and the more ley lines that link to the Place of Power the more powerful your ritual will be. Be careful because linking too many Ley Lines together may overwhelm the Place of Power causing a truly cataclysmic result, and conversely you can deprive a cabal or guild of their power source by severing the lines to them. Spells can resonate along ley lines providing effects at great range, but also echo like a spiderweb and alerting those perched along the same lines that a great ritual is being cast.

Their are other ways to generate power away from Ley Lines such as artifacts or profane ceremonies - royal sacrifices unleash the power of noble blood or defiling a site of holy power to siphon from the gods. The AI isn't afraid to fight you on these terms as well, and orders have received new possible agendas to safeguard Places of Power or keep the Ley Lines clean. As desperation mounts you may even find yourself on the receiving end of ancient powers, sure it may corrode their will but the devastation on your end may be impossible to recover from.