Spell Scroll

The barrage of fire and lightning had stopped, their mages apparently depleted. There wouldn't be a better chance for them to take the hill. They rushed out from behind the rocks, arrows landing amongst them. They formed up as quickly as possible and began their charge up the hill. It was too late. The sorcerers had already found and unfurled their scrolls, and fire rained down upon the exposed regiment.

Utility

Spell scrolls were originally developed by wizards as a means to store the magical energies of specific spells in a stable environment. These energies can be released by the mages at any time, giving them added flexibility in the spells available to them at any time. These mages can safely prepare their favorite or most used spells, without worrying about not having the right spell available for an unforeseen situation. Should one arise, they simply take out the spells scroll that solves the problem.
Wealthy lords kings and generals quickly came to the realization that these useful tools could be used to increase the number of spells their battlemages could cast during an engagement, greatly increasing their utility and lethality. Modern military engagements between forces of equal strength are commonly decided by which side can cast spells and hold off advancing foot soldier regiments the longest.
Regardless of the intent for the scroll, only those who would be capable of casting the spell without the scroll are able to deciper the texts and tap into the magic contained within.

Manufacturing

The creation of a spell scroll is an expensive and time-consuming process, so much so that most individuals will never be able to save enough coin to afford one. Scrolls are inscribed on vellum, parchment, or fine papers with ink that have been infused with the material components the spell normally requires to cast. The etchings, usually written in draconic, sylavan, or similarly ancient languages, hold the verbal and somatic components of the spell.