praesidium: the term meant garrison, and could be employed for a small outpost or a full-sized fort.

prefect: the commander of most auxiliary units was called a prefect (although a few unit COs held the title tribune). These were equestrians, who first commanded a cohort of auxiliary infantry, then served as equestrian tribune in a legion, before going on to command a cavalry ala.

procurator: an imperial official who oversaw the tax and financial administration of a province. Although junior to a legate, a procurator reported directly to the emperor.

res publica: literally ‘public thing’ or state/coomonwealth, this was the way the Roman referred to their state and is the origin of our word republic.

Roxolani: or ‘red alans’ were one group of Sarmatians, but are likely to have consisted of many subsections rather than a coherent and politically united tribe. At times they were allied with Decebalus, at times with the Romans, and often hostile to both.

sacramentum: the military oath sworn to the emperor and the res publica.

salutatio: traditional ceremony where people came to greet a Roman senator – and especially a governor – at the start of a working day.

Sarmatians: another blanket term used by the Romans and similar to the Greek use of Scythians. Reality was no doubt more complicated, but broadly speaking there were nomads originating from the Steppes. They were famed as formidable cavalry, employing bows and lances. Some were heavily armoured.

scorpion (scorpio): a light torsion catapult or ballista with a superficial resemblance to a large crossbow. They shot a heavy bolt with considerable accuracy and tremendous force to a range beyond bowshot. Julius Caesar describes a bolt from one of these engines going through the leg of an enemy cavalryman and pinning him to the saddle.

seplasiarius (or seplasiario): a military pharmascist working in a fort’s hospital.

sica: a curved, one-handed sword particularly associated with Thracians and Dacians. The edge was on the inside of the curve, like a sickle and like the larger falx.

signifer: a standard-bearer, specifically one carrying a century’s standard or signum (pl. signa).

Silures: a tribe or people occupying what is now South Wales. They fought a long campaign before being overrun by the Romans. Tacitus described them as having curly hair and darker hair or complexions than other Britons, and suggested that they looked more like Spaniards (although since he misunderstood the geography of Britain he also believed that their homeland was closer to Spain than Gaul).

spatha: another Latin term for sword, which it is now conventional to employ for the longer blades used mainly by horsemen in this period.

speculator: a soldier tasked with scouting.

tesserarius: the third in command of a century after the optio and signifer, the title originally came from their responsibility for overseeing sentries. The watchword for each night was written on a tessera or tablet.

thetatus: the Greek letter theta was used in some military documents to mark the name of a man who had died. This developed into army slang as thetatus meaning dead/killed.