The Elevation of the Cross commemorates both St. Helen's discovery of Christ's Cross in the fourth century, and its recovery from the Persians by Emperor Heraclius in the seventh century (at which time it was "elevated" in the Church of the Resurrection in Jerusalem).
From this victory celebration on, the "universal elevation" of the Cross was celebrated annually in all of the Churches of the Christian Empire. The day of the feast became the national holiday of the Eastern Christian Empire, and on that day it was "elevated" by the priests and bishops. The Cross served as the official emblem of the Empire, and was displayed on all building and uniforms.
The Troparion of the feast was sung on all public occasions, as a "national anthem" of sorts, and originally petitioned God to save the people, grant victory in war, and preserve the Empire "by virtue of the Cross". Today that Troparion, and all the hymns of the feast, are spiritualized: the adversaries are the spiritually wicked and sinful, including Satan and his armies, and the "Orthodox Christians" replace the ruling officials of the Empire.
This holy day, although is obviously has a political origin, remains with us as a day of prayer and fasting: the Cross is held up as the only symbol worthy of our total allegiance.