Saxo Educate Wartooth

10. 6. Meanwhile the Swedish king, Alver, died leaving three sons,
Olaf, Ingi, and Ingiald; Ingi, not satisfied with the inheritance from
lits father, declared war on the Danes so that he could extend his
empire. When Harald wished to investigate this event through the
oracles, he met an old man, very tall and with only one eye, wrapped
in a shaggy cloak, who said his name was Odin and that he was skilled
in the tactics of war; he offered Harald a most profitable lesson on
how to dispose his army in the field. Odin told him that when he was
about to make war with his land forces he should divide his entire
battle line into three squadrons; each of these he should pack in
twenties, but extend the middle section beyond the rest by a further
twenty men, arranging them to form the point of a cone or pyramid,
and should bend back the wings to create a receding curve on each
side. When a muster was held, he should construct the files of each
squadron by starting with two men at the front and adding one only
to each successive row. Thus he would set three in the second line,
four in the third, and so on, building up the following ranks with the
same uniform symmetry until the outer edge came level with the
wings. Each wing must contain ten ranks. Again, behind these
cohorts he was to introduce young warriors equipped with javelins;
to the rear of these he should place a company of older men to
reinforce their comrades, if their strength waned, with their own
brand of seasoned courage; a skilful strategist would see that slingers
were attached at the sides, who could stand behind the lines of their
fellows to assail the enemy with shots from a distance. Beyond these
he should admit indiscriminately men of any age or class without
regard for status. The final battalion he ought to separate into three
prongs, as with the vanguard, and deploy them in similarly proportioned
ranks. The rear, though connected to the foregoing columns,
might offer defence by reversing itself to face in the opposite
direction. If a sea battle should occur, he must divide off a section
of his navy, so that while the main fleet began the proposed skirmish
these other ships could skim round and encircle the enemy vessels.

10. 7. Once he had been drilled in this system of warfare, he
surprised Ingi and Olaf as they were preparing hostilities in
Sweden and stamped them out. When their brother Ingiald, under
pretence of ill-health, sent ambassadors to beg a truce, Harald
acceded to his demands, for, having in his manliness learnt to spare
those in misery, he was unwilling to vaunt himself over anyone
depressed by a period of low fortune. Later, exasperated by Ingiald’s
wrongful abduction of his sister, Harald plagued him with long,
indecisive wars, but finally took the other into his friendship,
preferring to have him for an ally rather than a foe.

- Gesta Danorum, Book VII