The buckler or daraq was a simple, small shield that was held in the hand (the reference to being strapped on to the forearm in the PHB is an error). It could only defend against one attack per round, and the hand could not hold a weapon. This design has, like most shields, been available since Ancient times, but was used mostly as a footman’s shield. Archers and mounted warriors had other types available to them. 

Small shields were often circular, made of metal or hide over wood. These too have been available since the Ancient period. Some designs backed the shield with padding, and suits of jousting armour in the later middle ages incorporated mounts for them into the left arm, some suits going so far as to actually build the shield into the arm itself. Other, later, designs merely expanded the shoulder plate until it covered most of the chest, forming a shield in it’s own right.

An example of the medium shield was the kite-shaped shield used by Norman cavalry. This shield was the most typical type for cavalry of the Dark and Middle Ages, and could be circular, kite-shaped (popular with horsemen as it’s tapered base meant that it could be held closer to the centreline of the body without snagging on the saddle), or lozenge-shaped. Padding was often incorporated into the backing of the shield to absorb the shock of blows and prevent fractures to the arm holding it. Oblong shields, curved in cross-section, were used by infantrymen (the most famous example being the Roman legionary), and gave more protection when used correctly in formation. Roman legionaries would form a “tortoise”, with the soldiers forming a square and the men on the perimeter holding shields at the front and sides (depending on where they were in the formation) and those in the centre holding their shields over their heads, in order to present an impenetrable shield frontage to the enemy. 

The body shield, also called a door shield (after it’s similar proportions) or pavise, was generally not carried by the individual. It was carried instead by a shield-bearer, whose task it was to protect his companion archer from enemy fire. It would generally be made of thick wood, with metal strips and studs for reinforcement. The bulk of material required to make it entirely out of metal would be far too expensive and heavy, and the absorbent properties of wood meant that it could be used without padded backing. If the user crouched behind it, it would completely obscure him from view. The surface of the door shield was often tarred and/or pitched to protect the bearer from boiling oil, hot ashes and other such things thrown by a besieged enemy on to their besiegers below. 

Shields for the battlefield often had designs worked into them, or could be painted with their owner’s coat-of-arms (if he had one). Parade-ground shields were much more ornate, covered with embossed figurines and carving. Such lavish decoration would not survive the rigours of the battlefield and so such shields were rarely used in combat.