The standard borne before the Roman emperors. It consisted of a gilded spear, with an eagle on the top, while from a cross staff hung a splendid purple streamer, with a gold fringe, adorned with precious stones. Constantine substituted a crown for the eagle, and inscribed in the midst the mysterious monogram.
(See Constantines Cross.) Rich (Antiquities, p. 361)
says “probably from the Gaulish lab, to raise; for Constantine
was educated in Gaul.” The Greek laba is a staff. (See
Source: Dictionary of Phrase and Fable, E. Cobham Brewer, 1894