Acrobats have been doing the somersault for years, and the word has been in the language at least since the sixteenth century.
It came to us from the Old French sombresault, which is from the Provengal sobresaut.
An obsolete English spelling of equal age is sobersault.
But to get back to the derivation.
The Provençal word is equivalent to the Spanish sobresalto, and this, in turn, comes from the Latin word supra, “over,” plus saltus, “jump.”
Thus to somersault is “to jump over,” or, in practice, “to jump over oneself.”