What cap was worn by slaves during an auction?

The cap worn by slaves during an auction was known as the pilleus. This was a conical felt cap that symbolized freedom and was often associated with newly freed slaves in ancient Rome. The use of the pilleus during auctions was significant as it visually distinguished slaves who were for sale.

The pilleus served as a reminder of the status of the individual wearing it; hence, when slaves were displayed for prospective buyers, donning the pilleus highlighted their position in society and functioned as a marker of their lack of freedom.

In contrast, the other options refer to different concepts in Roman culture. The titulus was a label that marked the status of a person, often placed around the neck of a slave to indicate their owner or their legal status. Vicarius refers to a substitute or deputy, typically used in administrative or military matters. Sportula, on the other hand, was a term used for a small basket or gift given as a form of charity or social welfare, often associated with patrons providing for clients or the poor, but not specifically related to the auction of slaves.