It frequently happens that in a mediæval picture of one of these machines some important mechanical detail is omitted, or, from the difficulty of portraying it correctly, is purposely concealed by figures of soldiers, an omission that may be supplied by reference to other representations of the same weapon. [Page 4] [Illustration: FIG. 1.--BESIEGING A FORTIFIED TOWN WITH A BATTERY OF CATAPULTS AND BALISTAS. _Criticism._--In this picture the balistas are fairly correct, but the catapults are too small. _From Polybius. Edition 1727._] [Page 5] It is, indeed, impossible to find a complete working plan of any one of these old weapons, a perfect design being only obtainable by consulting many ancient authorities, and, it may be said, piecing together the details of construction they individually give. * * * * * We have no direct evidence as to when the engines for throwing projectiles were invented. It does not appear that King Shalmaneser II. of Assyria (859–825 B.C.) had any, for none are depicted on the bronze doors of the palace of Balâwat, now in the British Museum, on which his campaigns are represented, though his other weapons of attack and defence are clearly shown. The earliest allusion is the one in the Bible, where we read of Uzziah, who reigned from B.C. 808–9 to B.C. 756–7. ‘Uzziah made in Jerusalem engines invented by cunning men, to be on the towers and upon the bulwarks, to shoot arrows and great stones withal.’ (2 Chronicles xxvi. 15.) Diodorus tells us that the engines were first seen about 400 B.C., and that when Dionysius of Syracuse organised his great expedition against the Carthaginians (397 B.C.) there was a genius among the experts collected from all over the world, and that this man designed the engines that cast stones and javelins. From the reign of Dionysius and for many subsequent centuries, or till near the close of the fourteenth, projectile-throwing engines are constantly mentioned by military historians. But it was not till the reign of Philip of Macedon (360–336 B.C.) and that of his son Alexander the Great (336–323 B.C.) that their improvement was carefully attended to and their value in warfare fully recognised. As before stated, the Romans adopted the engines from the Greeks. Vitruvius and other historians tell us this, and even copy their descriptions of them from the Greek authors, though too often with palpable inaccuracy. To ascertain the power and mechanism of these ancient engines a very close study of all the old authors who wrote about them is essential, with a view to extracting here and there useful facts amid what are generally verbose and confused references.