Frederick frequently led his military forces personally and had six horses shot from under him during battle. Frederick is often admired as one of the greatest tactical geniuses of all time, especially for his usage of the oblique order of battle. Even more important were his operational successes, especially preventing the unification of numerically superior opposing armies and being at the right place at the right time to keep enemy armies out of Prussian core territory. In a letter to his mother Maria Theresa, the Austrian co-ruler Emperor Joseph II wrote,