numerous books on drill and tactics. The first significant reference to the influence of Aelian in the 16th century is a letter to Maurice of Nassau, Prince of Orange from his cousin William Louis, Count of Nassau-Dillenburg on December 8, 1594. The letter is influential in supporting the thesis of the early-modern Military Revolution. In the letter, William Louis discusses the use of ranks by soldiers of Imperial Rome as discussed in Aelian's Tactica. Aelian was discussing the use of the counter march in the context of the Roman sword gladius and spear pilum. William Louis in a 'crucial leap' realised that the same technique could work for men with firearms. References Sources Ancient Greek writers Roman-era Greeks 2nd-century writers Ancient Macedonian army Ancient Greek military writers 2nd-century Greek people