The English seals, more finely and more artistically engraved than ours, give an excellent idea of the progressive development of the castles. Five of them show the sides of the ships as clinker built, while the seal of the city of _Poole_ makes the rivets really visible. The castles are so clearly shown in their successive phases of development, that any explanation is unnecessary. The steering oar, which is seen on the oldest seal, is replaced by a rudder on the others. The Boston seal shows a well turned out three-masted vessel with smooth sides. All the seals, save this last, show the forms of “cogs”, which proves once more the identity of the types of ships of the North-West of Europe. (Holmes states, on page 70 of his work, that the Poole seal gives the oldest English reproduction of a ship with a rudder, 1325.) As has been said already, the adoption of the compass was the signal for cutting loose from the coast and for undertaking more distant voyages. We learn, especially in the _Reygersbergh Chronijk van Zeelant_ (published by Boschhorn) Vol. II, p. 212, that about 1440, when the use of the compass had scarcely become general, the Zeelanders worked more and more toward the South, making toward Portugal and Spain. Before then, these countries seemed so far away that, when starting on a voyage thither, the seamen went to confession and the Holy Sacraments were received. At the same time with the invention of the compass, another event came to produce a great influence on shipbuilding; it was the invention of gunpowder, with the consequent adoption of artillery. The history of the Netherlands speaks for the first time of the use of artillery in connection with the expedition of Duke Albert against the Frisians in 1396. It seems, however, to have been used at the siege of the castle of Rozenburg-lez-Voorschoten, in 1351 (M. ~de Jonge~, Vol. I, p. 28). Cannon were not used either at the battle of the Sluis or in the maritime expeditions of King Richard III. But they were in general use on board ship in the XIVth century. (~Holmes~, p. 71.) The Genoese and the Venetians in the South, and the Hanseatic cities in the North, who were the masters of all peoples in commerce and navigation, were the first to adopt them. (M. ~de Jonge~, Vol. I, p. 29.) It was natural that artillery should modify war tactics and it can be said that the military value of ships depended on the number of guns which they carried. Finally, ships were built exclusively for war, and the practice of the Middle Ages, which was to utilize merchantmen for this purpose, must needs be abandoned.