The battle opened with a cavalry charge by both armies. The Spartan cavalry were quickly defeated by the superior Theban cavalry and were chased back to their own side. Their disorderly retreat disrupted the battle lines of the Spartan heavy infantry and, because of the resulting chaos and the dust stirred up, the Spartans were unable to observe the highly unusual advance of the Theban army until the last moment. Epaminondas had ordered his troops to advance diagonally, such that the left wing of the Theban army (with its concentration of forces) would impact with the right wing of the Spartan army well before the other weaker phalanxes. The furthest right wing of the Theban phalanx was even retreating to make this possible. This is the first recorded instance of the military formation later known as the oblique order. The Theban cavalry also helped by continuing to carry out intermittent attacks along the Spartan battle lines, holding their advance back.