In 614, the Sasanian general Shahrbaraz captured Jerusalem, massacred tens of thousands of Christians, and carried the relic of the True Cross — enshrined at the Holy Sepulchre since St. Helena's discovery in 326 — back to Ctesiphon as a war trophy.
Emperor Heraclius spent the next fifteen years rebuilding Byzantine armies and finally broke Persian power at Nineveh in December 627. Chosroes II was assassinated in February 628; the treaty that followed restored the Cross to the Empire.
On March 21, 630, Heraclius entered Jerusalem with the recovered relic. According to the ninth-century Chronicon Paschale, he tried at first to carry it in full imperial regalia and could not lift it; on removing his crown, purple, and shoes he bore it easily on his shoulders through the streets to the Holy Sepulchre. The Roman Martyrology commemorates the event on September 14 as the Exaltation of the Holy Cross.