hoplites carried a circular shield called a hoplon (often referred to as an aspis) made from wood and covered in bronze, measuring roughly in diameter. it spanned from chin to knee and was very heavy (8–15 kg). this medium-sized shield (and indeed, large for the time considering the average male height) was made possible partly by its dish-like shape, which allowed it to be supported with the rim on the shoulder. this was quite an important feature of the shield, especially for the hoplites that remained in the latter ranks. while these soldiers continued to help press forward, they did not have the added burden of holding up their shield. but the circular shield was not without its disadvantages. despite its mobility, protective curve, and double straps the circular shape created gaps in the shield wall at both its top and bottom. (top gaps were somewhat reduced by the one or two spears jutting out of the gap. in order to minimize the bottom gaps, thick leather 'curtains' were used but only by an [unknown] percentage of the hoplites, possibly mostly in the first row only since there were disadvantages as well: considerable added weight on an already heavy shield and a certain additional cost.) these gaps left parts of the hoplite exposed to potentially lethal spear thrusts and were a persistent vulnerability for hoplites controlling the front lines.