The size of the unit.
This number accounts roughly for this number of people:
0: one person
1: 8 persons
2: 30 persons
3: a group of 120 persons
4: an army of 500 persons
5: a horde of 2000 persons
When the attacking army is smaller than the defender then the defender gets extra defence dice for every point of difference in size. When multiple units are attacking the extra defence dice add-up for every attacker.
When one larger unit is attacking another unit they can try to swarm the other unit in a forced attack. This gives a plus 1 on the attack. When the unit is 2 or more points larger they get a plus 2. This cannot be used in combination with a combined attack. The forced attack does not work across city walls or fortifications.
