Shield shapes evolved over time, so it is not possible to give an answer to your question.
In the period 500 AD to about 1050 AD, round shields were the most commonly used type; then long, inverted-teardrop "kite shields" with round tops were used up to about 1160; then kite shields with flat tops were common up to about 1190; then slightly shorter shields became fashionable until the small "heater" shape became common by the middle 1200s (13th century).
Heater shields remained in use until the 1400s, when the use of shields gradually ended.
Throughout the medieval period, much larger shields called pavises were used by crossbowmen to protect them while reloading; these were free-standing tall shields with a hinged "leg" at the back that could be picked up and carried to a new position.
A Shield to Protect a Knight from injurys
shield volcanoes are in many places but the most common are the Hawaiian Islands
A knight needs a shield so that it can block things that are coming towards him. This is the Medieval wars.
The black death
A shield made of wood from a linden(basswood) tree.
In the medieval era. At least it is most common known to be in the medieval era.
An axe or a spear were possibly most common.
A shield and sword
Mantlet
soup
Wool would have been the most common material.
The most common disease is the ever popular plague.