So let’s start with some background context before we dive into Romans and purple: imagine that you’re a Roman citizen. There is a cabinet in your home. Usually right in the atrium, somewhere near the patriarch’s office. The shrine to the household gods is next to it, because it’s that important. In it are where your family keeps the death masks of all important family members. During funerals, your family hires actors to wear those masks and recite the deeds of all these important family members. Because in Rome, your family history and family greatness are the most important thing there is. One does not do anything to disgrace one’s family. Everything one does is to advance their personal greatness and family name.

Now let’s examine family structure. If you think of the structure of the mafia, this would come close to explaining the structure of a Roman family. At the head is the Paterfamilias. He controls everything that goes on in his household. To the point that when a child was born, the family held a ceremony where the child was put before the paterfamilias first acceptance. If the paterfamilias chose not to accept the child, it was left exposed outside the city walls (presumably for slavers to take). The paterfamilias is usually also a patron to other, less well off families. (Called clients). He in turn might also be a client to other, more wealthy patrons.

Getting back to reputation and family, This is why crucifixion was reserved for non-citizens who were the worst criminals. Because (in addition to being excruciatingly painful) such a public and humiliating death would bring shame on your family name. And by extension, any families associated with yours.

Now let’s examine why purple was a color reserved for the Emperor. Until the Industrial Age, the dye palate for clothing was very limited. The shade of purple reserved for Royalty was known as Tyrian purple. To make it, dyer’s in Tyre (modern day Lebanon) had to harvest a particular sea snail, crack open it’s shell and remove the digestive membrane. Then expose the mucus for a certain period of time. For all this work, they would get one drop of dye. It took around 250,000 mollusks to make one oz of useable dye. Because of this, the dye was worth it’s weight in gold.

What made it with the trouble was that the dye was vivid and color fast, so it would not fade. Depending on how it was used, the shade could range from scarlet red to blue-violet.

The rarity of Tyrian purple was what meant that the color was reserved for Royalty.

Now let’s get into sumptuary laws. Restrictive laws on dress date back to the time of the kings of Rome (and before that, in the classical period of the Greeks). There are laws written into the twelve tables.

In the days of the republic, Romans relied on dress to help identify who was important. There were very strict laws setting out who could wear certain clothes, and what they could be made of. (Called the Sumptuariae Leges). For example, non-citizens were forbidden from wearing togas.

Add to this that the toga was considered formal attire. Everyday wear in Rome was the tunic.

In the days of the senate, a senator was allowed to wear a toga trimmed in purple (toga praetexta). The number and width of the stripes varied based on one’s rank and office. (Wealthy equites could wear robes with a narrow Tyrian stripe. They had to possess 400,000 sesterces. For context, your average legionaries earned 900 sesterces a year. A new tunic during the time of Pompeii’s destruction was worth around 15 sesterces.)

If one was elected to the office of Censor (the high office), they wore a toga dyed completely purple for the duration of their office (Toga Picta). When a senator was elected to the office, it was often said of them that they took the purple.

Roman generals who were granted a triumphal parade were also allowed to wear a toga picta of purple and gold for the triumph.

In the time of the republic, cheaper shades of purple or indigo were allowed for the general public, (in Gaul, purple tunics made from dyed berries were given to slaves) and some women, such as priestesses were allowed to wear purple robes.

The tradition of wearing purple continued over to imperial Rome and later into Constantinople. In Rome, monuments to the imperial family were carved from a purple igneous rock called Imperial Porphyry.

A person born to rule was said to have been born to the purple (in the Great Palace of Constantinople, there was said to be a room covered in purple marble called the porphyry chamber in which the emperor’s heir would be born).

Additionally, sumptuary laws expanded under the emperors so that imitation shades of purple were forbidden, and only the emperor could wear it.

But this does not answer your question.

Assuming I’m a Roman citizen in the time of the republic. I’m aware of the sumptuary laws governing my dress, as well as the social and familial stigma attached to wearing purple when I am not entitled to it.

The first issue would be acquiring such a garment. This is before the days of fast fashion, so it would need to be purchased as dyed cloth and then created (for ultimate secrecy, in your domus by slaves) before you could wear it. If you are not the paterfamilias, you must go through him to have such a lavish drain of the household expenses approved.

Add to that, if you are going to wear a purple garment on the streets of Rome, it’s not going to be about showing off wealth or status. It’s a political statement (most likely treasonous) that is going to land you and your family in a bunch of hot water.

How much hot water is entirely dependent on that network of family connections.

Assuming you went out surrounded by the clients of your paterfamilias. They would act as bodyguards to keep outraged citizens from attacking you and beating you to death. You are wanting to make a political statement, so you head to the forum, where you can be seen and heard. Eventually, legionaries (edit: during the republic they would have been a Praetor and their armed guards. In the time of the Empire, they would have been Urban Cohorts, which were legionaries) disperse the crowd and take you into custody until the censor can decide your ultimate fate.

The clients of your paterfamilias rush back to your family domus to alert your paterfamilias (if he was not already there). He may contact his own patron (or patrons) and so on up the chain of influence to the senator or senators within your family’s sphere of influence. They may speak to the censor to argue for mercy on your behalf (or for your family, if they decide to cut ties to you after this).

Legally, Roman citizens couldn’t be crucified. But if the people involved in determining your punishment feel that your intentions are treasonous, you might be put to death by beheading.

Milder punishments might include (in order of seriousness) fines, loss of property, infamis (which includes loss of status, loss of legal protection, damage to your reputation, and inability to make a living due to said status), being made a slave (sent to the lead mines in Spain), banishment or some combination of these punishments.

As Rome shifted into imperial power, later emperors increased regulation so that even cheaper shades of purple were reserved for royalty. The “official uniform” for the emperor became purple silk garments. Under Alexander Severus, the state took control of the means of producing Tyrian Purple. Severus made it so that it wasn’t possible to purchase purple garments without his approval.