Depicted in various forms to express the will of God, of which they are the mediators. Shown as messengers, in worship, and in executing justice, they appeared in Western art before A.D. 600. Before Constantine their appearance without wings was mainly with a staff indicative of their office as messengers. The nine choirs are distinctively represented. Angels in art are represented with a variety of articles, musical instruments, thuribles, shields, scrolls, and in a few instances emblems of the Passion, though they are usually represented in worship before the Blessed Sacrament on earth and before the throne of God in heaven. Archangels are variously depicted: Michael driving Satan into hell; Gabriel announcing the Incarnation to Mary; Raphael healing the blind Tobit. The thrones are shown kneeling in adoration. Seraphim symbolize fire and love with their six red wings and eyes; cherubim with four-eyed wings of blue and holding a book, indicate their great knowledge; dominions, in royal robes, are crowned for authority; virtues, two-eyed, are charged with dispensing celestial miracles; the powers, holding swords, indicate their conquest of the evil spirits shown under their feet; the principalities carry scepters to assist in their direction of God's commands. The emblem of St. Frances of Rome is her guardian angel, whom she saw daily in visible form.