How is the symbol of the cross related to church architecture, theology, and art?

In the second century and the beginning of the third, Tertullian described the practice of making the sign of the cross: “At every forward step and movement, at every going in and out, when we put on our clothes and shoes, when we bathe, when we sit at table, when we light the lamps, on couch, on seat, in all the ordinary actions of daily life, we trace upon the forehead the sign [of the cross].”¹²⁴⁰ This custom was so familiar that the pagans of the second century accused the Christians of praying to the cross. However, Marcus Minucius Felix explained that this veneration was meant for Christ himself and not for the wood of the cross itself.¹²⁴¹ It is noteworthy that using the cross on a large scale in church buildings, in the fourth century, was a natural result of the appearance of a cross in the sky to the Emperor Constantine and the discovery of Christ’s cross by Constantine’s mother, Empress Helena. This marked the beginning of the widespread use of the cross in Church buildings.