WHEN, IN HIS PHILOSOPHICAL TREATISE DE RERUM NATURA, Lucretius discusses the optical effects of mirrors and considers why reflected images appear in perspective, he draws an interesting comparison. He writes that looking out a house doorway is akin to looking at a mirror: in both cases, a viewer sees one type of air and light, then an object (the door frame or the mirror), then a new type of air and light (outside the house or the reflection), and, finally, the real objects outside the house or the reflection in the mirror. The technicalities of Lucretius's argument (such as light brushing the eyes) leave something to be desired, but it is notable that, when Lucretius wants an example of two distinct spheres, he turns to the spaces inside and outside a house. The former was prone to spotlighting the chief resident and establishing hierarchies among visitors, while the latter was characterized by the challenging of social boundaries. Yet these two strikingly diverse spaces were immediately adjacent. Only a wall of masonry stood between them. This chapter investigates that architectural interface.

House façades made up much of the street's border and therefore lent much to the space's visual experience. In Chapter 4, as we recognized the close ties binding house to owner and mapped Roman concerns for both exteriority and visibility, street architecture emerged as a means of personal presentation, particularly in the arenas of domination and control, literal or symbolic. The evidence of sidewalks, ramps, and street-axis views already speaks to a careful consideration of how streetgoers encountered houses and how architecture entered into the street's contestations. Our understanding of houses’ power to shape the street deepens when we turn to house façades’ specific forms and how they mediated between interior and exterior, individual and communal, protection and display.

If Romans like Lucretius sensed the inside–outside disparity innately, they also experienced it daily. Streetgoers who peered through an open house door might have spotted any number of sumptuous decorations. At Pompeii's famous Casa dei Vettii (VI.15.1), to give an opulent example, their view encompassed a verdant garden, a trickling fountain, finely wrought furniture, and elaborate murals (Fig. 37).