Ninjas of the ancient Roman Empire

Question

The emperor needs a way to quickly and decisively kill his enemies (Romans and non-Romans). So he devised an assassin squad to carry on his devious intentions.

• Kill or hijack enemy VIP personnel and leadership.
• Destroy important buildings.
• Sabotage enemy infrastructure.
• Spread false information.
• Lower the morale of the enemy troops.
• Sabotage ships at port.
• Spy on enemy formations, tactics, technical advances.
• Bribe people.

Question:

How would Roman ninjas be armed and armored? What kind of social element should be entrusted with this task?

Answer 1

History review

As commented, it's not because we are unaware of ninja squads that there were none. There were certainly no lack of feats associated with ninjas. I am not sure however that a specific group was made to accomplish all the tasks. We can look over some of them

• Assassination of VIP. Well, at Rome, I think, it can be considered national sport to butcher your neighbour. If we consider the tip of the iceberg, namely the Emperors, you can have a look at the cause of death of Roman Emperors, or a reduced list specificially looking at known or alledged assassinations. As you can see, they were quite creative, with a certain liking to poisons. Your Emperor's squad, would definitely have to research some of the most subtil poisons. From those sources, it appears that most of the kills were made by relatives of the target. So you probably need a good information to "help" those relatives make the "right" choice. And thus get...

• Spying. Spying is of course two fold: get information in wartime about your enemy location and forces, but of course, at all time, get information on who's likely to try to kill you next amongst your friends.

  • Information collection on your population. In a short search I did not find much information, but a note shows a certain preference for "elaborate spy network[s]". Furthermore, "each senatorial family had its own private intelligence network" as per here.

  • Military Intelligence. This website seems to corroborate @o.m.'s answer. MI by the Romans seems to rely on the following squads: equites are scouts riding horses ahead of the legion; exploratores are also horse-riding scouts but operating at larger ranges; speculatores are covert agents. We get further that

    Speculatores might be soldiers, citizens, slaves, etc. In short, anyone who might be able to infiltrate enemy towns and positions, while doing so undetected. They might infiltrate enemy positions by posing as deserters, refugees, merchants, and so on.

    This other website, shows another example of speculatores as

    Around 300 b.c., for example, during the Etruscan wars, the consul Q. Fabius Maximus sent his brother disguised as an Etruscan peasant into the Ciminian forest to win over the local Umbrians to the Roman cause. The brother was both fluent in Etruscan and a master of disguise. He was sent to reconnoiter areas into which Roman agents were said never to have penetrated. The mission was a resounding success, and Rome was able to bring Umbrian tribes into an alliance.

    or

    Quite frequently intelligence couriers doubled as political assassins

• Sabotage. The Romans had a very effective army. So combined with the MI from above, they had a decisive advantage. I couldn't find any illustration of military sabotage.

• Terrorism. The commonly accepted first terror actions was made by a sub-group of the Jewish Zealot in 1st Century. Apparently they were known for carying hidden daggers (sicarii) to "greet" the Roman citizens.

I think by now, I have covered most of what you want from your Ninja squad.

Ninjas

From the elements above, your ninjas, should have

• ability to disguise well,
• possibly have a good language knowledge for remote operations,
• the (urban-)knowledge of different classes to infiltrate more effectively their target,
• martial knowledge: Spanish swords and daggers,
• knowledge of different poison: effective, yet discreet,
• the typical military tactics knowledge.

Discussion

This is not exactly your question, but as it seems, the Roman were more relying on networks as squads. There are a few interesting points to consider to explain that.

• The Empire is very centralized (as opposed to feodal Japan). And extremely large. It is much easier to organise a consistent network than a polyvalent squads which should be too large (consider the travel time!), or not so effective.
• Politics. The honour system of the Roman Empire is very different that the one of Japan for the Ninja-time. How do you make sure that your informant are reliable? Indeed if you create such a squad, it is "easy" for your ennemies, to just reverse the squad allegiance, and get you out of the way.

Some further elements of discussion are also included in the already cited website. I recommend you to read the exhaustive illustration of that site.

_{I don't know the reliability of the sites I used to illustrate this answer, but the different ones I have found seems to be consistent.}

Answer 2

Expanded in response to bilbo_pingouin:

Consider the agentes in rebus, Imperial messengers and agents of the late Roman Empire. They operated openly within the Imperium, delivering orders and conducting inspections. People like that would have to be reasonably respectable, perhaps equites. It would be easy to imagine them a little more gung ho.

Or the speculatores. Initially military scouts, as bilbo_pingouin wrote, there were examples of them becoming Imperial bodyguards. Going with the origin of the speculatores, they might well have been outsides to the "regular" power structure of Rome, so they can't be tempted to meddle in power games themselves.

Foreign mercenaries? Perhaps from the east, not from the north?

Freedmen? They would be familiar with Roman culture, unlike barbarians, but unable to scheme for power in their own right.