To whit (from Wikipedia):
Plutarch records that the Sacred Band consisted of 150 homosexual couples, the rationale being that lovers could fight more fiercely and cohesively than strangers with no ardent bonds. According to Plutarch's Life of Pelopidas), the inspiration for the Band's formation came from Plato's Symposium, wherein the character Phaedrus remarks,
And if there were only some way of contriving that a state or an army should be made up of lovers and their loves, they would be the very best governors of their own city, abstaining from all dishonour, and emulating one another in honour; and when fighting at each other's side, although a mere handful, they would overcome the world. For what lover would not choose rather to be seen by all mankind than by his beloved, either when abandoning his post or throwing away his arms? He would be ready to die a thousand deaths rather than endure this. Or who would desert his beloved or fail him in the hour of danger?—
The Sacred Band originally was formed of picked men in couples, each lover and beloved selected from the ranks of the existing Theban citizen-army. The pairs consisted of the older "heniochoi", or charioteers, and the younger "paraibatai", or companions, who were all housed and trained at the city's expense. During their early engagements, in an attempt to bolster general morale, they were dispersed by Gorgidas throughout the front ranks of the Theban army.
After the Theban general Pelopidas recaptured the acropolis of Thebes in 379 BC, he assumed command of the Sacred Band, in which he fought alongside his good friend Epaminondas. It was Pelopidas who formed these couples into a distinct unit: he "never separated or scattered them, but would stand [them with himself in] the brunt of battle, using them as one body." They became, in effect, the "crack" force of Greek soldiery, and the forty years of their known existence (378–338 BC) marked the pre-eminence of Thebes as a military and political power in late-classical Greece.
The Sacred Band under Pelopidas fought the Spartans at Tegyra in 375 BC, vanquishing an army that was at least three times its size. It was also responsible for the victory at Leuctra in 371 BC, called by Pausanias the most decisive battle ever fought by Greeks against Greeks. Leuctra established Theban independence from Spartan rule and laid the groundwork for the expansion of Theban power, but possibly also for Philip II's eventual victory.