What Does “With Your Shield or On It” Mean?
It means come back victorious or come back dead. A Spartan carried his shield home from a victory and was carried home on it as a corpse. The one option it rules out is running away, because a man who fled threw his shield away first.
The line is preserved by Plutarch in the Sayings of Spartan Women (Moralia 241F), where a mother hands her son his shield as he leaves.
The threat is specific, and it is about the shield rather than courage in general. Spartan armour was personal, but the shield was the one piece that protected the man standing beside you as much as yourself. Dropping it to run was the one unforgivable act, and the word for a man who did it, tresas, marked him for life.
A tresas kept his citizenship in name and lost it in practice. He was not spoken to, not married into, and expected to go about in a cloak of patches with half his beard shaved (Plut. Ages. 30; Hdt. 7.231).
Plutarch is writing centuries after Sparta's peak, and the sayings collections are a late genre. The sentiment is consistent with everything earlier sources describe; the exact wording may be polished.
Further in
Acenes of Sparta: The Dragon Slayer
A dragon is the reason the 300 died. Leonidas used the magic of the gods to bind Kalaxes beneath Taygetus, and the price was his life and his men's. Sixty-two years later a seven-year-old of the agoge falls into the dragon's crypt and inherits the unpaid balance.
Free to read with Kindle Unlimited. Open it on Amazon.