This is just an overview of some Eastern Roman (Byzantine) military equipment through the ages. this is part 1, the early Empire.
Early Period
Infantry
Early East Roman soldiers were clad much differently from their Augustan and Princepian counterparts. Gone was the Lorica Segmentata, scutum. Replaced with cheaper and more easily manufactured shields and armor. The famous caligae sandals replaced by Gothic boots. The classic gladius short sword replaced by the longer Spatha.
Shown here are typical Eastern Roman Infantryman a 4th to 6th centuries AD.

As you can see, the traditional rectangular scutum shield has been replaced by an oval shield. Instead of the Pila, he carries lighter javelins or small lead weighted darts called plumbata or martiobarbulli .
The legionary is also armed with a stout spear as his primary weapon to ward off cavalry. Instead of the testudo formation of earlier eras, the East Roman legionary was trained to form the foulkon . The foulkon was formed by interlocking shields and sticking the spears outwards , sort of a hybrid of the testudo and the Ancient Greek Hoplite phalanx . The infantry were specially trained to make gaps in the line for friendly cavalry to charge through and surprise the enemy. At the command of "Appear spaces!", the legionarys would form 3 foot wide gaps in the line for the heavy cavalry to charge through and decimate the enemy infantry. As quickly as the spaces would appear, the infantry line reformed and continued the assault.

For protection, he wears a lorikon of either chain or scale mail. Only the front line soldiers would be equipped so heavily however, with legionarys in the middle of the line protected with only their shields and padded or leather armor. His helmet is a mass produced "ridge" helmet, with crosses cut into the helmet to show the Empire's religion and to lighten the helmet's weight. Instead of the gladius, he is armed with the Spatha (or spathion in Greek) longsword, an influence from the large amount of Germanic soldiers in the army. the Spatha gave the legionarys a longer reach when fighting, and also more penetrative and slashing power due to the increased weight.
The skirmisher is equipped with only a shield and tunic. He wears no armor so his speed is not hindered in battle. Skirmishers would be equipped with a variety of weapons including Javelins, slings, plumbata darts and bows. And also a sword if close combat duty was needed. The main role of the skirmishers was to harass and pepper the advancing enemy with projectiles from in front of the line of infantry. When enemy infantry or cavalry would come close, the skirmishers would retire behind the friendly infantry line and continue their assault from there. Skirmishers were also used to lure opponents into traps and ambushes.
Cavalry

The main offensive arm of the Eastern Roman army was it's super heavy cavalry. Referred to as either Cataphractii, meaning "covered in armor" (Kataphraktoi in Greek) or Clibanarri, meaning "Oven men" (Klibanophoroi), these soldiers were inspired by the Sassanian Persian soldiers of the same name. Horse and rider are covered from head to toe in armor. The first layer of armor for the rider would be padded cotton armor, to absorb shock and provide a barrier between the armor and skin. The second layer would be the chain mail lorikon , and the third would be the scale or lammelar klibanion .
Usually, a small round shield would be strapped to the left arm while the right was used for fighting. The Cataphracts carried a variety of weapons. Sometimes, the riders would carry plumbata darts in a saddle bag and harass the enemy before charging. A short spear was carried for the initial charge, after which a heavy mace or the Spathion was brought to bear for close quarters melee.
The Eastern Roman army also employed Horse Archers in their armies, usually of Hunnic or nomad stock. They would wear their native garb while fighting for the Empire, and sometimes would adopt some Roman armor, but never anything heavy as speed was essential for their role on the battlefield. In Belisarius' campaigns in Africa and Italy, the Hunnic horse archers were an essential part of the order of battle. They would be armed with the Hunnic or eastern composite recurve bow. The small size of the bow made it ideal for shooting on horseback. And even though the bow's size was small, it's materials of sinew and horn would be able to deliver the same amount of force as a full sized all wooden bow, in a smaller package.
Sources
Maurice's Strategikon
"Warfare,State and society in the Byzantine World"- John Haldon
http://s_van_dorst.tripod.com/lrarmy.html
http://warandgame.wordpress.com/2008...e-roman-armor/