This area covers warding and shielding in various forms, from personal to large-scale buildings. In addition, for those who are capable of doing it, dispelling magic and null field spells are possible at higher degrees of specialisation. Defensive magic takes up a significant part of the syllabus in the first year of study, as it gives the student mage the ability to protect him or herself during their other studies.
All mages leave college with the ability to cast a personal ward around him or herself. This gives a basic protection against magical attack, although to add protection against mundane attack as well is a second spell. Personal wards need to be refreshed every couple of days, otherwise they decay. One thing to note, however, is that the shield will not stop the effects of momentum: for example, if a shielded mage is hit by a bullet, the shield will stop the mage taking damage from the bullet, but is still likely to knock him over.
A mage also leaves college with the ability to created more substantial but shorter-duration shields, and to ward individual buildings.
The shield is pretty basic - rather like a mundane shield, of a certain size that must be pointed in a certain direction. The mage can decide if the shield is against magical or mundane attacks, but at basic level it cannot be both without running up a second spell. Moreover, while it prevents anything getting through to the mage, equally the mage cannot try to cast a spell or fire through it in return, or it will bounce back.
In a magical society, where mages can scan into many areas, privacy is a major concern. Warding at this level will protect a building against a fair degree magical scanning and interference, although it isn't completely foolproof. However, it does not protect the actual structure of the building.
Also, any mage gains the ability to dispel or cancel the duration of his own spells.
Personal wards become more versatile and easier to cast, such that both magical and mundane attacks can be defended against with a single spell, and the ward only needs refreshing about once a week. However, the issue of momentum remains.
For shielding, the main development is into a shield that can be shaped more easily, and can defend against both physical and magical attacks with the same spell, although the mage does need to give a little of his concentration to keeping the shape and properties otherwise it will drift slowly back to a basic shield.
In addition, it is possible to make modifications onto basic shields, for example to use them to try and damage the opponent's weapons in a mĂȘlée.
For warding, the improvements come in either the strength or the coverage of the wards. A ward could be strengthened so that all but the very strongest mages are kept out of a building. Likewise, wards of the more basic level could be extended over an entire complex of buildings. In addition, limited protection against magical or physical intrusion becomes possible - such as basic alarms - and some resistance to damage to the structure of the building is achieved.
Dispelling running spells set up by other people becomes possible, although this has to be done at fairly close range, and the mage needs to be of at least equal skill and mental ability to the mage that cast the spell for it to work. Of course, as spells do decay over time, the longer they have been running, the easier they are to dispel - again, depending on the strength of the caster.
Personal wards become second nature, and can be left running with minimal input from the mage - maybe a quick refresh once a month or so. Moreover, momentum can be neutralised to an extent, depending on the circumstances.
With shielding, the shield becomes second nature: it just runs, and does not need any further input from the mage.
For warding, whole complexes can be strongly warded. In addition, wards can help protect the structure of buildings. In addition, alarms begin to be more complex: from "intrusion" to "intrusion in this room".
Dispelling magic becomes easier, not needing to overcome the skill of the caster in the same way, and also a "null field" is possible - all spells running in an area are neutralised (note, both caster's and target's), including racked spells.
This field is mainly used in times of war, where mages are expected to protect a city and its inhabitants from outside attack, for example in the "Blitz" in 1940. It also includes elements of high level investigative magic. Included are spotting incoming magical attacks, and working out range and target, and quick-cast large-scale shielding spells, which can be put up temporarily to protect, say, an area of buildings which are the target of an incoming magical attack. In addition, the very best defensive mages of this sub-specialisation can actually intercept incoming magics and render them harmless: effectively shooting down magical "bombs", etc.
Relative to standard defensive wards, the difficulty is making the jump from those to the kind of scale involved in large-scale warding (say a house to a city block, and even a whole neighbourhood). So while it is it relatively simple to incorporate some of the methods of building large-scale defensive wards into normal warding (which can also include ritual elements, if the mage has the time and skill to include them), getting the size is something else again. In addition, the personal energy of the caster also remains connected to the wards, in a way that isn't the case with normal wards, which are 'fire and forget', such that the caster can reinforce the wards when they come under attack, if he or she is in a position to do so, and that will strengthen them against a particularly major attack.
Security magic is a further development of warding and alarms. Spells can be set which, when broken or triggered, sound audible alarms and can not only alert the mage (or other person specified when the alarms are set up), but give him full details of what has happened, and can actually have an effect on the person unwise enough to break the trigger (for example an electric shock, or the release of a gas).