What can one say? A spear is a knife on a stick, the base level foot soldiers weapon par excellence since the most ancient times. The middle Byzantine era kontarion came in two sizes. The short kontarion was about 2.4 metres long. The great kontarion was between 4 and 5 metres long.1 The two upright men in the picture below are armed with great kontaria, while the lunging man deploys a menavlion. Whereas Nikêforos Fôkas gives a specific size for the head of a menavlion, spear heads only needed to be fit for the task. Front line infantry carried the great kontarion, while the short kontarion was the armament of cavalry and lighter infantry.
1   Spears are discussed with sizes in all the Byzantine military manuals of the tenth century. On the subject of interpreting the sizes of equipment given in the military manuals see Timothy Dawson, Fit for the Task: Equipment Sizes and the Transmission of Military Lore, sixth to tenth centuries, Byzantine and Modern Greek Studies, 31 (2007). Download a PDF copy.