The most precious relic preserved by the Byzantine church was the "True Cross", claimed to be the actual cross on which Jesus Christ was crucified. Discovered in the 320s during the renovations of the pilgrimage sites in Jerusalem under Helena, mother of Constantine the Great, the Cross had been venerated by generations of pilgrims by the seventh century.
In 614 AD the unthinkable occurred. The Persians, in one of their periodic resurgences of military power, invaded the Byzantine East, as the avengers of the deposed and murdered emperor Maurice Tiberius. They reached Jerusalem, besieged and took it, looting and pillaging the pilgrimage sites. As part of their triumph over the unbelieving (non-Zoroastrian) Christians they carried away the Cross to Ctesiphon; its capture was taken by them as a sign of the weakness of Christ against Ahura-Mazda.
The Cross remained in Persian hands for fourteen years. Meanwhile the emperor Heraclius, having disposed of the usurper Phocas, whose actions caused the problem, prepared his counterstrokes. In 628 AD his army, invading from Armenia, defeated and destroyed the Persian military might. Now the tables were turned; the Byzantines recovered what they had lost, with interest. The Cross was returned to its place of honor in Jerusalem.
The Cross remained in Jerusalem for a further five centuries. Used as a standard in battle by the Crusaders, it was captured at Hattin in 1187 by the Muslims. Eventually, so the story goes, it was taken to the Great Mosque in Cairo, where it was placed under the entrance so that all the Muslim worshipers walked over it on their way to prayers.
Tokens were issued as souvenirs of the celebrations accompanying the return of the Cross to Jerusalem in 630 AD. They are small clay or terra-cotta "medallions", made by pressing a lump of clay into a (probably wooden) mold. It is said that a piece of the wood of the Cross was burned and the ash mixed with the clay; hence the tokens, themselves, became miniature reliquaries.
The tokens were produced in two main types. The classic design is the standard True Cross reliquary design: the Cross, with or without base, held by Constantine in imperial robes on the left side and Helena in robes and widow's veil on the right. Two subtypes are known: first, a variety with two Xs, probably intended as stars, above the arms of the cross, and second, with the cross on steps, much like that on the reverses of many Heraclian coins. The second type shows a Greek cross with the letters H N E I in the angles. Exactly what this Greek inscription means is not certain; the most likely reading is hn ei(dos), "behold the appearance (of the Cross)".