Do nothing at all without the beginning of prayer. With the sign of the living cross, seal all your doings, my son. Go not forth from the door of your house till you have signed the cross. Whether in eating or in drinking, whether in sleeping or in waking, whether in your house or on the road, or again in the season of leisure, neglect not this sign; for there is no guardian like it. It shall be unto you as a wall, in the forefront of all your doings. And teach this to your children, that heedfully they be confirmed to it.
(St. Ephrem the Syrian – d. 379AD, from Let Us Attend: Reflections on the Gospel of Mark for the Lenten Season, p. 77)