Through the kind efforts of the same queen, the cross of the Lord was then found. It could not, of course, be consecrated at the beginning, owing to the opposition of the Jews, and afterwards it had been covered over by the rubbish of the ruined city. And now, it would never have been revealed except to one seeking for it in such a believing spirit. Accordingly, Helena having first got information about the place of our Lord's passion, caused a band of soldiers to be brought to it, while the whole multitude of the inhabitants of the locality vied with each other in seeking to gratify the desires of the queen, and ordered the earth to be dug up, and all the adjacent most extensive ruins to be cleared out.
Ere long, as the reward of her faith and labor, three crosses (as of old they had been fixed for the Lord and the two robbers) were discovered. But upon this, the greater difficulty of distinguishing the gibbet on which the Lord had hung, disturbed the minds and thoughts of all, lest by a mistake, likely enough to be committed by mere mortals, they might perhaps consecrate as the cross of the Lord, that which belonged to one of the robbers. They form then the plan of placing one who had recently died in contact with the crosses.
Nor is there any delay in carrying out this purpose; for just as if by the appointment of God, the funeral of a dead man was then being conducted with the usual ceremonies, and all rushing up took the body from the bier. It was applied in vain to the first two crosses, but when it touched that of Christ, wonderful to tell, while all stood trembling, the dead body was shaken off, and stood up in the midst of those looking at it. The cross was thus discovered, and was consecrated with all due ceremony.
Source: Sacred History (New Advent)