Okay I’m gonna need out here a bit but this is actually SUCH a cool coin.
So to start with, you've gotta understand that you could just mint coins in the Roman Republic. Currency wasn't standardized, so if you had enough influence and enough wealth to actually make the coins out of (such as if you were a conquering general), you could just design a coin for use as propaganda and then pay all your soldiers using it. This gets very popular in the later years of the Republic.
Despite this, however, it took until 82 BC for the first Roman to put himself on a coin. The man who did was Lucius Cornelius Sulla Felix — the same Sulla who won the first large-scale civil war in Roman history and became the first man in Roman history to seize power by force, reviving the office of dictator. He was the last to hold the dictatorship before Julius Caesar, to put things in perspective.
It's worth noting that Julius Caesar himself was the first Roman to put his own head on a coin. This is kinda a big distinction from Sulla's coin:
where the obverse (the front side, here shown on the left) is the head of Roma, the personification of the Roman state, and Sulla himself is only shown on the reverse, and there only as part of a scene of action.
To contrast, here is Julius Caesar's coin:
where on the obverse is the head of Caesar, surrounded by the text CAESAR DICT PERPETUO, or "Caesar, Dictator for Life". It is no small wonder that this coin is known as "the coin that killed Caesar".
A small note on the office of dictator: in contrast to the modern definition, a Roman dictator was a formalized (though extraordinary) office of the state. When the Roman state faced a threat that could not be handled by its normal magistrates for some reason, a dictator was appointed. When dealing with the specific threat they were appointed to counter, they had power exceeding that of all other magistrates, though still subject to oversight from the Senate and the tribunes of the plebs. When the crisis was resolved, the dictator would immediately resign their powers. There were numerous dictators in Roman history who dealt with their respective crises and then peacefully gave up their powers, so the office itself wasn't inherently destructive to the state.
Anyway, so this is all to say that for someone allegedly trying to restore the Republic, by putting his own head on a coin Brutus is getting off to a rocky start. But regardless, let's take a closer look at the coin:
I've put pictures of both gold and silver examples of the coin — these are more readable examples than the photo shown in the tweet.
On the obverse, we see the head of Brutus, along with the text BRUT IMP and L PLAET CEST. The latter refers to Lucius Plaetorius Cestianus, who struck the coin (it's typical to see some mark indicating who minted the coin on Roman coins). The former is short for BRUTUS IMPERATOR, or "Commander Brutus".
Another side note, this time on the title Imperator. The modern association of the term is with emperor, and while this became true with the foundation of the Roman Empire, it was not yet true in Republican Rome. During the Roman Republic, the title of imperator was an honor given to a commander by their troops after an especially great victory. It did not simply indicate that the commander has authority over their troops, but was a great honor that they had to earn in the battle. The earning of the title imperator allowed the commander to receive a triumph from the Senate, which was an immense honor, one which also made commander who received them extremely popular.
As Brutus was never hailed as imperator nor did he ever receive a triumph, the usage of IMP on this coin is clearly an attempt to spin the assassination of Caesar as a victory in battle worthy of a triumph.
Moving on to the reverse, it has a pileus, or freedmen's cap, surrounded by two daggers. Underneath are the words EID MAR, short for Eidibus Martiis, or "On the Ides of March". Obviously, the daggers refer to the actual killing of Caesar. The pileus is interesting because of its deep ties to freedom in the minds of the Romans. As part of the ceremony upon the freeing of a slave, the former slave's hair was shaved and a pileus was placed upon their head. Thus it had a deep association with gaining liberty, one only reinforced by the fact that it was a symbol of the goddess Liberty herself. One source even claims that the assassins "bore a [pileus] on the end of a spear as a symbol of freedom" as they left the Senate chambers crying to the world that they had slain a tyrant who aimed to make himself king (Appian, The Civil Wars, II.119). Brutus' inclusion of the pileus on the coin clearly aims to further cement the connection between the death of Caesar and freedom.
The part that I personally find coolest, however, lies with the inscription. As noted above, "eid mar" is short for "eidibus martiis". This is the ablative form of the Ides of March (the ablative case in Latin is used for, among other things, indicating when something occurred ["ablative of time when"]). However, what's interesting about it is that eidibus is the archaic spelling. The contemporary way to spell it would have been idibus martiis, shortened to ID MAR, with the exact same meaning. Brutus' use of the archaic form hearkens back to the days of old, attempting to connect the killing of Caesar with a return to the "good old days" of the Roman Republic.
evidently this didn't work out so well for Brutus, but it's a fascinating coin.
