In some scenarios the defender may set up fortifications. All fortifications must be represented on the board by a suitable model.
There are many forms of fortifications, but broadly they represent cover for the defender. Sandbagged positions, trenches, redoubts, makeshift barricades and fortress walls all count as fortifications. The defender may set up as many fortifications as he likes and the scenario set up rules explain where these fortifications can be placed – usually in the defender's deployment zone.
A model in fortifications receives a cover saving throw of 4+, see the Rules Book for more information on cover saving throws.
In addition to cover there is a special type of fortification called bunkers. See Bunkers for the full rules.