Wards are the simplest magic known to the Nephilim, along with glamour. There are several variations of wards, all of which serve as a shield meant to keep something in or out of a certain area. They exist in different levels of power, and may be put up through spells, runes, or may even be naturally existing.
The world is separated from the dimension of the demons by wards. While demons are able to pass through the wards and into the human dimension, the wards make it difficult and strenuous for them, thus keeping out the vast majority of demons and protecting the world from a complete invasion. However, due to the continuous Incursion, the wards have slightly thinned, it is said that more and more demons are getting through the wardings.
Shadowhunters have wards at their disposal, given to them by the Angel Raziel, the first being the wards he placed around Idris, preventing the country's discovery by mundanes, who are incapable of passing through wards, while allowing Downworlders and Shadowhunters to do so without difficulty. If a mundane passes through the Idris wards, he will be transported instantly to the corresponding location on the opposite border.
In Alicante, the wards are supported and controlled by the demon towers surrounding the city. The magic of these wards disrupt modern technology and prevent electricity and similar power sources, machinery and Marked firearms from working reliably within its borders, resulting in the need for witchlight to power the city, and why communications are made primarily through letters and fire-messages—though the weaker wards of Institutes typically do not cause this problem. These wards have proved too complicated for the Nephilim to comprehend enough to enable them to recreate or duplicate elsewhere, or even modify or alter.
Demonic magic has its own wards, which work similarly, such as the pentagram used by warlocks to summon demons, which they draw up with demonic runes.
With the research and secret magic in the Gray Book, the first generation of Silent Brothers were able to create Shadowhunter wards. These wards are weaker versions of Idris' and the world's wardings, though have proven efficient for their own uses. These wards are similar to glamour, in that they divert certain individuals away from a place or an object, done through illusion or distraction. Wards may also be made complex and specific as to who is warded and who is allowed through.
Other simple uses of wards include the protection of small area, such as a single room or an object, like a locked chest, or even a ship, like what Valentine did to his to be able to sail through the East River undetected by the Clave and warlocks.
However, another way to circumvent the wards is reverse-warding. Being reverse-warded means having Marks that block it off as a place outside the protection of wards. Two known reverse-warded areas are the Sanctuary of Institutes and Portals.
In the case of Sanctuaries, since the gates of the Institute typically prevent vampires and demons from entering the sacred land of the Institute, the Sanctuary is reverse-warded to become the only room where they can enter. Meanwhile, Portals, which are drawn with demonic runes that cancel out the wardings, are reverse-warded, enabling it to bypass wards, particularly in Idris, thus making it one, if the the only, way for mundanes to enter the country, on the rare occasion when it became necessary.
For an unknown span of time, the world had already been warded from the Void. Over the years, however, because of Sammael and Lilith's combined efforts and the Incursion, more and more demons have reached the human world, the wards no longer able to keep them off in numbers. When Raziel gave the Shadowhunters their country with a warding protecting it, the first Silent Brothers studied the wards and successfully learned to replicate a lesser version of the wards for their kind. They performed rituals all over the world, intending to reinforce the power of the wards with their own.
For the first known time in history, the wards of Idris were taken down by Sebastian Morgenstern with his demonic blood as a part of Valentine's plans. As a precaution, wards were also placed around Lake Lyn that would alarm the Clave if anyone Portaled into it. However, Valentine also took this down when he arrived.