or followed-up by cavalry. In the 16th century, a lighter, less expensive cavalry gained ground, so that the proportion of cavalry in the armies actually grew continually, so that in the last battles of the Thirty Years War cavalry actually outnumbered infantry as never before since the high feudal period. Another change that took place in the late 15th century was the improvement in siege artillery as to render old style fortifications very vulnerable. But the supremacy of tactical offence in siege warfare was not to last for very long. As Philippe Contamine has noted, by a dialectical process which may be found in all periods, progress in the art of siege was answered by progress in the art of fortification, and vice versa. Charles VIII's invasion of Italy in 1494 demonstrated the potency of siege artillery; but in this region by the early years of the 16th century there were beginning to emerge fortifications which had been designed specifically to resist artillery bombardment. The full impact the 15th-century "artillery revolution" was blunted fairly quickly by the development of the bastion and the trace italienne. But the military supremacy which the possession of a powerful siege train conferred contributed in no small degree to that strengthening of royal authority which we find in some European states in the later 15th century. Size of armies The increase in army size and its influence on the development of Modern States is an important point in the military revolution theory. For example, Spain's army increased from mere tens of thousands in the late 15th century to 300,000 regulars and 500,000 militia (paper strength) by 1625 spread all throughout Europe, according to Philip IV.<Ref>Martin Hume. The Court of Philip IV: Spain in Decadence." Londno 1907, p. 157. Quoting Philip IV's address to the Council of Castile in 1626. "Last year, 1625, we had nearly 300,000 infantry and cavalry in our pay, and over 500,000 men of the militia under arms, whilst the fortresses of Spain are being put into a thorough state of defence. The fleet rose at one time in 1625 to 108 ships of war at sea, without counting the vessels at Flanders, and the crews are the most skillfull mariners this realm ever possessed. This very year of 1626 we have had two royal armies in Flanders and one in the Palatinate, and yet all the power of France, England, Sweden,