Scenes of Roman camp building, with tents inside and defended entrances, are shown several times on Trajan's column, clearly indicating the importance of “castrametation” to the Romans. Polybius's long digression on camps formed one of the important elements of military studies from the Renaissance period on, with analysis of the text beginning at least as early as the fifteenth century. During the campaign season, when the army was regularly on the move, it constructed a camp at the end of each day's march, as attested by many literary references throughout the Roman period. Important for the future survival of the army, as well as its morale when fighting, the baggage and support activities were protected in the camp. The physical form of camp entrances can be established from archaeological evidence.