The Army
The Roman Army created in antiquity all the essential methods that have come to define the military machine the world over. In antiquity the infantry had been the effective core of the army, with cavalry being an auxiliary force. With the adoption of the stirrup in the later sixth century that changed rapidly, and by the beginning of the seventh century increasingly heavily armoured cavalry became the cutting edge of an expeditionary force, with the infantry serving as a support structure in field operations. Infantry, of course, retained their importance in siege warfare on both sides of the walls.
The enduring Roman Empire of the tenth to twelfth centuries did not rely on regular standing armies to the degree of the early Empire. In the earlier part of this period, when campaigns were fought, regular standing units based in the capital and major cities, and often called hetaireia, formed a nucleus for larger forces levied from country (“thematic”) families owing pronoia, that is to say, military service in exchange for tenure of agricultural land.
The sources are silent on the precise composition of the standing urban hetaireiai. It seems likely that they would have comprised both cavalry and infantry in order to retain a balanced reservoir of skills and knowledge to bring to both elements of the thematic levies.
From the eleventh century especially, pronoia obligations were increasingly converted to a cash equivalent, which the imperial treasury then used to hire manpower, often from outside the Empire. The Roman Army had, of course, been a destination for such negotiable fighting men since the early imperial era, but sometimes it was not just a matter of money. Anna Komnênê, writing of the late eleventh century said that amongst the English service in the Roman military was an “ancestral trust”. Doubtless the elite of Constantinople would like to think it was inherited from the days of the Roman occupation of Britain, but it was probably rather more recent. There is good evidence that the Roman authorities had been actively recruiting in England from at least the beginning of the eleventh century. The men who answered that call went into various branches of the military, regular units as well as distinctly “mercenary” ones. This background must have influenced the response of some English to 1066, for it is well attested that in the wake of the Norman Conquest, there was significant English emigration to the Empire. Not only did warriors join various units of the Roman army and navy, but so many joined one of the palace guard units, the Varangians, that by the end of the eleventh century it was commonly known as “the English unit”. And it was not just men of the military class who left England for the Empire, but also significant numbers of farmers and family groups, who were settled on vacant imperial lands, particularly along the Black Sea coast.
Large scale contacts between Constantinople and Britain continued through the period covered by the Hetaireia Palatiou, and Britons remained a notable group in the Roman military. Following the Battle of Myriokefalon against the Turks in 1176, which had gone badly, Emperor Manuel wrote to King Henry II lamenting the deaths of “so many valiant Englishmen” serving in the Roman army.
The Navy
Constantinople has always been a city that depended on the sea. Needless to say, it served as one of the Empire's greatest naval bases. The Book of Ceremonies mentions that on some occasions Marines (Ploimoi) did ceremonial guard duties as well as the hetaireiai. A document detailing the logistics for a tenth-century expedition to Cyprus enumerates the equipment to be provided for each ship including that of the marines, showing that just as today they were regarded as an elite service, being provided with arms and armour equivalent to front line cavalry troops on land.