Just pulling together some thoughts after a Twitter conversation, (collected here on my Storify of footprints), with @rogueclassicist and @Caroline Lawrence. We've had a least one similar conversation before. The question of the function of footprints on tiles, if there was one, has been focus of the debate, and the possibility of an apotropaic function seems to be at the heart of it in my recollection.
[caveat - I checked my ancient citations and the Poggio Civitate reference because they were quick and easy, the rest comes from my imperfect memory]
A variety of footprints have been identified pressed into the top (always?) surface of roof tiles/tegulae. Many of these are the tracks of animals, but there are also human footprints ranging from the small prints of children to those of adults.
I suspect that the animal tracks are accidental, created by animals wandering across tiles as they are laid out in the open to dry before firing. The/some of the human footprints perhaps represent a different phenomenon. Human footprints could be accidental. For example, at the Etruscan site Poggio Civitate there are human prints preserved in roof tiles laid out in the workshop to dry. This structure was destroyed by an accidental fire and in a rush to flee the burning building, people ran across the still soft tiles. The form of the tracks indicates that these individuals were running. (E. Nielsen, 1991) But not all prints suggest an obvious and accidental reason for their presence.
Recent excavations conducted by the Sangro Valley Project have produced a tile fragment preserves traces, albeit faint, of boot print with hobnails. There is nothing about this impression that suggests rapid movement, or even an actual step being taken. Should we imagine that someone was loitering about and decided to push his foot into the tile just because he could?
In addition to the footprints of adults, there are a number (how many?) of tiles that preserve the footprints of children. Now, surely children are likely to push a foot or a hand into a drying tile just to do it. But this then begs the question of whether children were present in tile production areas. This could be an interesting area of research into the lives of children and the spaces they inhabited in the Roman world. One could also imagine that perhaps these are the footprints not of free born children but perhaps the children of slaves.
If, however, these prints are not accidental or minor incidents of vandalism, why are they on tiles? One possible reason for these impressions is apotropaic. Could these footprints represent religio-magic attempt to ensure either a successful firing process or to add a layer of protection to the roof constructed from the fired tiles, (or even a combination of both)?
In Roman culture there is an apotropaic/good luck function associated with human feet. In Petronius’ Satryicon (30.5), we see Ascyltos and Encolpius admonished by a slave to step into Trimalchio’s dining room with dextro pede. Roman brides were customarily carried over the threshold of their new husbands’ homes to ensure that they would not misstep and bring bad fortune to the marriage right at the start. Vitruvius (de Architectura 3.4) also comments that temple staircases are designed with an odd number of steps to ensure a fortuitous arrival on the podium.
By the time of the Roman Empire terra sigillata vases were being impressed with maker’s marks in the form of a footprint, planta pedis (literally the “sole of a foot), typically containing the name or initials of the manufacturer. Why do these manufacturers’ stamps take the form of a foot? Is it for good luck in the firing process?
Any other thoughts out there? Any references? Other examples of footprints on tiles?