But we will leave a subject whose complicated details would lead us too far, and return to the equipment proper of vessels. As far back as the tenth century, the Emperor Leo originated the practice of building towers for attack and defence on the deck of the dromons; these towers, from the centre of which sprang the mainmast, reached half-way up the mast. This custom was still observed in the thirteenth century, and was no doubt handed down from very ancient times when it was usual to build towers and citadels on the decks of triremes. The round class of vessels were also provided with towers, one fore and another aft. In the smaller vessels these towers were simply platforms surrounded with a crenulated parapet and raised upon pillars (Fig. 89); in the larger ones, the towers were constructed of several stories added to the normal elevation of the poop and prow. Mangonels, catapults, and other projectile machines were placed on these towers and platforms. The big ships especially carried terrible engines of destruction, sometimes a heavy beam which worked horizontally like an ancient battering-ram against the sides of a hostile vessel, sometimes an immense bulk of timber, which was worked vertically from the top of the mast in order to shatter and sink a smaller craft. Around the masts, too, and nearly at their tops, _châtelets_ or platforms were suspended, in which were hidden, behind a low parapet, slingers, archers, and stone-throwers. In the sixteenth century, these châtelets on board the vessels of the Mediterranean were called _cages_ or _gabies_, while in the North sailors designated them by the Icelandic term of _hunes_ (Fig. 90). [Illustration: Fig. 90.--Seal of the Town of Boston (1575), on which the _hune_ is depicted at the extremity of the mast.]