Collegium, Brotherhood of Rogues - Collegium

Shortlisted for the 2022 Chaucer Historical Fiction awards - Based around historically factual events. Book #1: Collegium of Rogues:  Egypt has fallen, Cleopatra and Antonius are dead by their own hands and Octavius Caesar is now the most powerful man on earth. But Caesar's position is far from secure, with enemies in the Senate plotting against him and renegade legionaries still loyal to Antonius fermenting rebellion, among them, the renegade legate of the Third Aegyptus, Titus Eximius, who, sworn to topple the young tyrant, escapes from Egypt and turns to the Barbarians of Moesia to raise a Celtic army to invade Italy, financed by a vast treasure hidden by Marcus Antonius years ago.
Titus has no idea that Caesar's legions are secretly poised to conquer Moesia to secure the empire's frontiers along the mighty Danube. Meanwhile, in Rome, an insidious group of senators and political enemies led by Fannius Caepio are plotting Caesar's assassination, but they know they're powerless without military assistance, and so, an alliance is made between the plotters and the Antonians, who are set on rekindling the bloody civil war.
Sabinus, the ennobled blood son of the infamous and villainous Grassator (gangster) First Centurion of the Fifth Macedonica, Nepos Maximo, the Bastard of the Aventine. Sabinus is also the adopted son of the patrician adventurer Draco Cerialis, a one of Caesar's best spies and commander of the "Irregulars, " a small band of elite Speculatorii (behind enemy lines special forces). After the fall of Egypt, Draco and the Irregulars are sent to hunt down and kill Titus Eximius and destroy his renegade legion.
When Draco is killed in an ambush, Titus escapes to Byzantium. Sabinus vows vengeance against Titus who is responsible for Draco's death and Caesar's spymaster, Gnaeus Domitius Calvinus puts Sabinus in command of the Irregulars and sends him to hunt Titus down and to find Antonius fabled "Syrian gold" (Antonius's hidden war chest). Meanwhile, the Greek and Macedonian legions invade Moesia, and Sabinus with his half dozen Irregulars pursues Titus Eximius into war-torn Moesia, the reluctant commander of two cohorts of regular troops, battling their way through a formidable enemy to rendezvous with the Fifth Macedonica.
Teutonius, with his officers has joined King Budorix of the Triballi, a warlike Moesian Celtic people who lay between the Fifth Macedonica and its prize - the fortified city of Ratiaria on the Danubius River. King Budorix has amassed a massive army of barbarian allies and intends to stop the Romans and drive them back to Macedonia and the two armies come face to face in a bloody and violent battle, upon which hangs the success or failure of the conquest and Sabinus's prize, Titus Eximius and the eventual fight to the death between two bitter enemies, only one will survive.