The sixth-century bureaucrat John Lydus wrote that Roman military dress had changed over time but that there were still some troops who dressed in the manner of Aeneas. These were known as the excubitores and they’d been established in the reign of Tiberius (de Mag. 1.12). The same author claimed the emperor Leo the Great was the first to place them at the side-exits of the palatium and noted they numbered “three hundred in accordance with ancient custom” (1.16).
This unit can be traced to the siege of Alesia (52 BC) when Caesar’s camp included twenty-three towers guarded by excubitores at night. But they then fell off the map, only popping up like moles with varying roles among the guard regiments. These units, which started off as the personal forces of generals, had by 27 BC morphed into a permanent guard for the princeps. The praetorians were also established as a corps (with their own command structure and barracks) but they were separate from the (mainly Germanic) imperial bodyguard known as the Batavians.
A single praetorian cohort and its tribune formed the main palace guard. Only the tribune was able to enter the imperial bedchamber. These wore togas, not regular military dress. Part of this cohort (labelled speculatores) had different functions. They numbered three hundred and were essentially praetorians promoted to special duties. It was one of their number who killed Otho (69).
John the Lydian implied the excubitores were related to the vigiles (de Mag. 1.12) created by Augustus after the great fire of AD 6. The vigiles divided their 7,080 freemen into seven cohorts of c. 1000 under the command of a praefectus vigilum. Part of each cohort was dedicated to guard duty of their respective regions stationed in a guard-house (excubitorum). For the excubitores of the tenth region their main role was to guard the domus Augustana Augustana et Tiberiana.
By Trajan’s reign a further imperial corps was formed: the equites singulares Augusti led by the praetorian prefect. This amounted to the praetorians effectively taking over the old “Germani custodes” i.e. the old mounted bodyguard. Comprising c. 500 men, their camp was located near the Lateran (where they remained until the mid-third century before being disbanded by Diocletian’s scholae, though they may have lingered on until Constantine’s reign to be terminated after the battle of Milvian Bridge). Another unit were the unambiguously labelled “protectores” who had units assigned to the palace called “protectores domestici” shortened to “domestici.”
These, however, are all background noise for the reappearance of excubitores in Constantine’s reign. Indeed, it is hard not to feel sorry for the junior eunuch who the emperor placed in his bed when he discovered his father-in-law Maximian had told his daughter to leave the door ajar for an assassin. After all, it was only when the conspirator had skewered the bed’s occupant that Constantine emerged with a gang of scholae. According to Lactantius this episode occurred at the connivance of the excubitores.
At the Bosporus the part (just inside the main ceremonial entrance) of the imperial palace named “exkoubita” was almost certainly named after the excubitores and formed their HQ. While at the Seine, their western counterparts policed the Parisian equivalent according to Marcellinus in his account of Julian’s acclamation (360). Indeed, the author was one of the aforementioned “protectores” assigned to senior generals (Uricinus in his case). Furthermore, Marcellinus described how – acting on a false rumour of Julian’s assassination – troops descended into anarchy at the palace. In the commotion that followed they had to confront the excubitores.
During Julian’s life the political strength of these guard units grew. Indeed, on his deathbed the protectores domestici proclaimed Jovian emperor (a man who’d been tribune of the guard). Jovian’s successor in turn was a Scholarian tribune while his brother Valens was protector domesticus. But while their politics waxed, their military strength waned. Adrianople (378), for instance, was largely lost after Valens ignored the advice of his senior general Sebastian who demanded the scholae palatinae receive more training before battle.
There is no further mention of the excubitores until the mid-late fifth century with the exception of Nilus of Ancyra who wrote to an excubitor called Isidore (ep. 2.372 = PG 79, col. 357). But the sources are also silent about other units we know existed such as the candidati (an elite subgroup of the bodyguard) and decani (a unit within the domestici peditum). That said, units were rarely rigid identities. The firefighting function of the vigiles for instance was transferred to the collegiati in the time of Valentinian I (though their security functions remained). Their “night prefect” was abolished by Justinian, too, who admitted nobody seemed to know “how” the title had become associated with duties that had little or nothing to do with the nocturnal hours. Instead the role was adorned with a new label: “praetor of the people” (Novel 13, praef).
The excubitores appear to have constituted the elite guard element to the 1,000 members of the scholae stationed in Constantinople (total strength: 3,500). These palace guards got a bad rap from contemporaries. Prokopios mentioned that since Zeno they had been recruited from “cowards and unwarlike men” (Anekdota, 24.17). Agathias, too, mentioned that Zeno “enrolled his own compatriots who had no military experience whatsoever and ultimately just his mates.” If they were a little militarily useless (NB there’s no obvious signs of dysfunction) they were still politically potent. A comes excubitorum for example (Justin) famously became emperor.
They certainly weren’t always to be found idling around the palace. Indeed, when pagan Italy forced the bishop Autonomus into exile in Bithynia c. 300, he settled in Soreoi on the Gulf of Nicomedia. Initially he was successful in converting locals and dedicated a large church to the archangel Michael. Diocletian’s officials, however, eventually issued an arrest warrant and he fled to Claudiopolis on the Black Sea. When he returned similar circumstances forced him to leave for Limnae. There, however, he met his fate and was stoned to death by enraged pagans during Divine Liturgy. This digression might appear a little too tangential were it not for the fact that an excubitor named John found his relics c. 490 perfectly preserved on the site of his martyrdom (Acta Sanctorum, sept., vol. 4, 18 [PG 115, col. 696]).
In the same year (490) the excubitores throttled the patrician Pelagius on the orders of Zeno. Eight years later the same men descended from the kathisma into the hippodrome to kill a Moor who’d thrown a stone at the emperor Anastasius (Malalas, Chronicle, 16.4). Justin was probably comes excubitorum when his companions were called to repel the seaborne attack by Vitalian in 515. And when Anastasius died there was a standoff between the scholae and excubitores over the successor, a contest the latter clearly won.
Indeed, some comites excubitorum played rather theatrical roles that echoed the old maestro Sejanus – though thankfully not his death considering his body was mangled by a crowd on the Gemonian steps (d. 31). Priscus, for example, was annoying enough to be banished by Theodora (529), Theodorus was murdered while on a secret mission in Carthage (533), and Marcellus gained tremendous influence under Justinian. Later, Corippus noted that the first officials to greet and acclaim Justin II (565-574) at the palace were the excubitores. He explained that they guarded the entrances of the palace (In laudem Iustini Augusti minoris, I. 202-206):
“Excubiae primum, quae summa palatia servant,
Imperium felix dominis intratibus optant
Et cunctos aditus armato milite vallant,
Ne quis in Augustam contrarie audeat aulam
Infensum conferre pedem.”
Later, an Avar legation was confronted by
“The great excubitors… who lined the long porticoes…
linking their golden shields… all glittering equally…
towering as leafy oaks amid sacred rivers… the
sacred palace with its officials is like Olympus.”
Corippus described them as brandishing battle-axes (bipennes) and wearing high-laced boots known as “cothurni.” John Lydus portrayed Aeneas as having black-greaved boots known as “crepidae” (1.12) and implied they were still worn by the excubitores. This is corroborated by Paul the Silentiary who described an imperial procession of excubitores donning black boots (HS ekphrasis, 261).
It wasn’t all ceremony of course. The excubitores defended the Thracian Long Walls against the Avars in 600 (Theophylact Simocatta, Historiae, 7.15.7). And a series of commanders gained military experience before being elevated to the throne. Tiberius II for example was comes excubitorum, as was his successor Maurice (who also took on a senior military post on the Persian frontier). Eventually Leo III downgraded the comes in the hierarchy but Constantine V elevated him again and resurrected the unit as part of the imperial tagmata. In a neat little ouroboros, the excubitores appear to have been replaced at the palace by the vigla i.e. a reconditioned vigiles, the main unit from which they had once sprung.