mid-13c., portraien, "to draw, paint" (something), from Anglo-French purtraire, Old French portraire "to draw, to paint, portray" (12c.), literally "trace, draw forth," from por- "forth" (from Latin pro-; see pro-) + traire "trace, draw," from Latin trahere "to drag, draw" (see tract (n.1)). Meaning "depict in words, describe" is from late 14c. Related: Portrayed; portrayer; portraying.
Latin protrahere was "to draw forth" but in Medieval Latin also "to draw, paint."