Line infantry was a type of infantry that trained and organized to fight in linear formations, usually arranged two or three ranks deep, to deliver coordinated volleys of musket or rifle fire. This method of warfare began in the late sixteenth and early seventeenth centuries, with its origins commonly attributed to reforms by Maurice of Nassau and the Dutch army. Dutch practices were soon adopted by other European armies and became widespread through military manuals, the movement of officers, and the training of foreign troops by Dutch instructors. Further development occurred in the eighteenth century under leaders such as Frederick the Great of Prussia, who refined drill, discipline, and the use of concentrated musket fire. His methods made the Prussian infantry a model for other European powers. The tactics and organization of line infantry reached their most widespread application during the Napoleonic Wars, when massed ranks of soldiers firing in volleys formed the core of European armies on large battlefields.