There are several types of Marches boosters, but beware that if you activate several at the same time only the same type can be used! If you start a different type the previous booster is canceled.
These boosters must be activated BEFORE you start any marching.
Note: This only raises the troops you can send in one march - it will not magically give you more troops.
Troop enlargement by 25%
One type available, are active for 12h. Cost 5000 Gold.
Troop enlargement by 50%
Two variants, one that is valid for 15 minutes (given as reward, can not be bought) and one that is valid for 12h (10000 Gold).
Troop enlargement by 100%
One type, are active for 12h. Only available in package deals (needs verification).
See also Shrine of Odin.
Related topic: Marching Speed-up