barrel was due to improvements in both iron technology and gunpowder manufacture, while the development of trunnions—projections at the side of the cannon as an integral part of the cast—allowed the barrel to be fixed to a more movable base, and also made raising or lowering the barrel much easier. The first land-based mobile weapon is usually credited to Jan Žižka, who deployed his oxen-hauled cannon during the Hussite Wars of Bohemia (1418–1424). However, cannons were still large and cumbersome. With the rise of musketry in the 16th century, cannon were largely (though not entirely) displaced from the battlefield—the cannon were too slow and cumbersome to be used and too easily lost to a rapid enemy advance. The combining of shot and powder into a single unit, a cartridge, occurred in the 1620s with a simple fabric bag, and was quickly adopted by all nations. It speeded loading and made it safer, but unexpelled bag fragments were an additional fouling in the gun barrel and a new tool—a worm—was introduced to remove them. Gustavus Adolphus is identified as the general who made cannon an effective force on the battlefield—pushing the development of much lighter and smaller weapons and deploying them in far greater numbers than previously. The outcome of battles was still determined by the clash of infantry. Shells, explosive-filled fused projectiles, were also developed in the 17th century. The development of specialized pieces—shipboard artillery, howitzers and mortars—was also begun in this period. More esoteric designs, like the multi-barrel ribauldequin (known as "organ guns"), were also produced. The 1650 book by Kazimierz Siemienowicz Artis Magnae Artilleriae pars prima was one of the most important contemporary publications on the subject of artillery. For over two centuries this work was used in Europe as a basic artillery manual. One of the most significant effects of artillery during this period was however somewhat more indirect—by easily reducing to rubble any medieval-type fortification or city wall (some which had stood since Roman times), it abolished millennia of siege-warfare strategies and styles of fortification building. This led, among other things, to a frenzy of new bastion-style fortifications to be built all over Europe and in its colonies, but also had a strong integrating effect on emerging nation-states, as kings were able to use their newfound artillery superiority to force any local dukes or lords to submit to their will, setting the stage for the absolutist