Obstacles are things like hedges, fences, walls and trenches that troops must clamber over to cross. Although obstacles may be similar in some respects to difficult ground, in that a hedge and a wood might both contain trees, there is an important difference. Obstacles are basically linear barriers, such as a wall, which troops must cross over before they can proceed. Difficult terrain describes an area of ground such as a bog or marsh that slows down overall speed.

It takes a model half of its movement phase to cross an obstacle. So if a model has a move of 4" it must surrender 2" to cross a hedge or a wall. If a model has insufficient move left to cross an obstacle it has reached, then it must halt in front of it. The model does not count as half way across if it has 1' of its 4" move remaining, for example. Where an entire unit of troops is attempting to cross an obstacle the penalty continues to apply to the whole unit so long as any of the models are crossing.

It is not uncommon for the front of a unit to end up on one side of a linear obstacle and the back to be on the other side. This is fine. Place the part of the unit which has crossed on the far side of the obstacle and leave the part that has yet to cross on the other side. As long as the ranks on both sides are in contact with the obstacle this is perfectly acceptable. Once troops have moved over the obstacle the unit's ranks are returned to base contact. Remember that the unit suffers a half move penalty until all its troops have crossed the obstacle.

If a wall, hedge or fence has a gate in it then it is assumed to be open unless otherwise agreed, and troops may move through the gate without penalty.

If a unit's formation is divided by an obstacle then it may not manoeuvre by turning or wheeling, and it may not change its formation. The unit must cross the obstacle before it can do any of these things.

Bear in mind that a unit of troops can suffer the reduced speed for moving over difficult terrain and the half move penalty for crossing an obstacle. If troops are moving at half speed of 2" across difficult terrain, across a freshly ploughed field for example, then they must still surrender a half their move phase to cross a hedge or fence, a -1" penalty in this case.