614 -- How the True Cross Was Lost

Saint Helena with the Cross, Lucas Cranach the Elder, 1525 (Cincinnati Art Museum) (source)

The frontiers of the Roman Empire (Constantinople)  in 600 AD.

Classical Antiquity

600 BC -- 530 BC --- The reign of Cyrus II (Cyrus the Great) as Shah of Persia. Approximate date commonly ascribed to the life of Zoroaster (Zarathustra) by modern historians. Persians of late Antiquity, however,  believed he had lived in the time of the Hellenistic Seleucid Empire, which rose in 312 AD.

63 BC -- Roman conquest of Palestine.

Late Antiquity

326-328 AD -- Pilgrimmage of Roman Empress (Saint) Helena (mother of Constantine the Great) to the Roman Holy Land, founding churches and establishing relief agencies for the poor. At the time, Rome was still a pagan Empire.

Historians Gelasius of Caesarea (died 395) and Rufinus (died 411) claimed that she discovered the hiding place of three crosses that were believed to have been used at the crucifixion of Jesus and the two thieves, St. Dismas and Gestas, executed with him. To one cross was affixed the titulus bearing Jesus's name, but Helena was not sure until a miracle revealed that this was the True Cross.

335 AD -- Consecration of the Church of the Holy Sepulchre in Roman Jerusalem.

590 AD --  Khosrow II (Khosrow II), son of Hormzid IV, succeeds his father as Shah (King) of Persia at age twenty.

591 -- The usurper Bahram attempts to overthrow Khosrow II as Shah, using apocalyptic imagery from the millennium of Zoroaster.

Bahram tried to support his cause with the Zoroastrian apocalyptic belief that by the end of Zoroaster's millennium, chaos and destructive wars with the Hephthalites/Huns and the Romans occurs and then a savior would appear. (The Persians at the time believed that Zororaster had lived in the Hellenistic Seleucid Dynasty, a claim that is not accepted by contemporary scholars of Zorastrianism).

591 -- The Roman Empire Maurice helps restore Khosrow II to the throne of Persia after the coup attempt by Bahram.

602 -- Murder of Maurice by the usurper Phocas. Khosrow II odeclares war on the Roman Empire (Constantinople) in revenge.

After the Byzantines killed Maurice, Khosrow II began a war in 602 against the Byzantines. Khosrow II's forces captured much of the Byzantine Empire's territories, earning the king the epithet "the Victorious". 

608 -- Heraclius the Elder, a Roman General in North Africa, leads a successful revolt against the usurper Phocas. He and his son, Heraclius the Younger, establish a new government based in Carthage. They conquer Sicily and other nearby territories.

609 -- Heraclius the Younger sails from Carthage eastward to confront Phocas in Constantinople.

As Heraclius approached Constantinople, he made contact with prominent leaders and planned an attack to overthrow aristocrats in the city, and soon arranged a ceremony where he was crowned and acclaimed as Emperor. When he reached the capital, the Excubitors, an elite Imperial Guard unit led by Phocas's son-in-law Priscus, deserted to Heraclius, and he entered the city without serious resistance. When Heraclius captured Phocas, he asked him "Is this how you have ruled, wretch?" Phocas's reply—"And will you rule better?"—so enraged Heraclius that he beheaded Phocas on the spot. He later had the genitalia removed from the body because Phocas had raped the wife of Photius, a powerful politician in the city.H

610 -- Formal Coronation of Heraclius as Roman Emperor in Constantinople. He begins a series of disastrous military campaigns against Persia, resulting in the loss of major Roman territories.

610 -- Persians conquer the remaining Roman parts of Mesopotamia (Iraq), as well as the Roman regions in the Caucasus Mountains.

611 -- Persians overrun Roman Syria.

614 -- Aided by local Jews, the Persians take Roman Jerusalem. They damage the Church of the Holy Sepulcre and take the True Cross back to the Persian capital Ctesiphon as a prize.