From the time of the introduction of cast-iron cannons in 1558 until a comparatively late period, development in naval artillery proceeded at a very slow rate. The security that was attained by the adoption of cast-iron was so great, as compared with the danger attending the use of the more ancient artillery, that the new guns were regarded as fully supplying all the demands of a suitable battery. The guns were muzzle-loaders, making the manipulation simple, the previous rude attempts at breech-loading being abandoned. The number of calibres that were introduced was very numerous, partly to suit the weight of the batteries to the ships, and partly to accommodate the fancy of the time for placing in different parts of the ships guns varying much in size and destructive effect. The general character of the batteries and the multiplication of calibres can best be illustrated by noting the armament of two typical ships of the seventeenth century. [Illustration: BRONZE BREECH-LOADING CANNON CAPTURED IN COREA, AGE UNKNOWN.] The _Royal Prince_, a British ship built in 1610, carried fifty-five guns. Of these, two were _cannon-petronel_, or 24-pounders; six were _demi-cannon_, medium 32-pounders; twelve were _culverins_, 18-pounders, which were nine feet long; eighteen were _demi-culverins_, nine-pounders; thirteen were _rakers_, 5-pounders, six feet long; and four were _port-pieces_, probably swivels. These guns were disposed as follows: on the lower gun-deck, two 24-pounders, six medium 32-pounders, and twelve 18-pounders; on the upper gun-deck the battery was entirely of 9-pounders; and the forecastle and quarter-deck were armed with 5-pounders, and the brood of smaller pieces which swelled the nominal armament. The _Sovereign of the Seas_, built in 1637, in the reign of Charles I., was unequalled by any ship afloat in her time. She mounted on three gun-decks eighty-six guns. On the lower deck were thirty long 24-pounders and medium 32-pounders; on her middle deck, thirty 12-pounders and 9-pounders; on the upper gun-deck, “other lighter ordnance;” and on her quarter-deck and forecastle, “numbers of murdering pieces.” In the obstinately contested actions between Blake and Van Tromp in the Cromwellian time, the ships and batteries did not differ in any great degree from those contemporaneous in construction with the _Sovereign of the Seas_; and when we remember the inferior character of the powder used in those days we can account for the duration of some of the engagements between the English and Dutch ships which were sometimes protracted through three days. [Illustration: BRONZE BREECH-LOADER USED BY CORTEZ IN MEXICO.]