Staurogram

The Staurogram (⳨), also Monogrammatic Cross or Tau-Rho, is a ligature composed of a superposition of the letters tau (Τ) and rho (Ρ).

The Staurogram was first used to abbreviate stauros (), the Greek word for cross in very early New Testament manuscripts such as P66, P45 and P75, almost like a nomen sacrum, and may visually have represented Jesus on the cross.

The Tau-Rho as a Christian symbol outside its function as nomen sacrum in biblical manuscripts appears from c. the 4th century, used as a monogramma Christi alongside the Chi-Rho and other variants, spreading to Western Europe in the 5th and 6th centuries.

Ephrem the Syrian (4th century) discusses a Christian symbol, apparently combining the Tau-Rho with Alpha and Omega placed under the left and right horizontal arms of the Tau. Ephrem says that the Tau represents the cross of Jesus (prefigured by the outstretched hands of Moses in ), the Alpha and Omega signify that the crucified Christ is "the beginning and end", and the Rho, finally, signifies "Help" (βοήθια [sic]; classical spelling: ), because of the numerological value of the Greek word being 100, represented by Rho as a Greek numeral.

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