Essentially, the rum is a metallic "lining" of the end of the keel; but it had also a long point with a high piercing capacity. Thus, a strong keel is needed able to resist the big shock at its end. To this end two prerequisites are needed: The resistance of this keel and its appropriate connection with the surrounding wooden parts of the ship.
Regarding its resistance, the characteristic case ofthe "Argo" ship is worth noting (Apollonius Rhodius, A' 125): "And immediately, both the Pagassae harbour and the Argo herself shouted urging them to start their voyage: since on the Argo a sacred timber had entered, a wood [cut] from the [sacred] oak of Dodona and fitted by Athena into the inner part of the forward keel'". This passage shows the fundamental role of a strong keel - part of a holy-tree of Zeus in this case.
Now, according to the second prerequisite, the shipbuilders should cast a ram being hollow in its rear part, and with a geometry compatible with the end of the keel which would penetrate into the ram.
- Let us now see in more details a representative sample of ancient rams:
This ram (dated probably the 4th cent. BCE) of total mass of ca. 80 kg in its integral form, is made of bronze (with a high tin percentage of 11,7%) and follows the typical morphology of the external three cutting carvings. It is instructive to compare the longitudinal section of this ram with the posterious gigantic ram of Althlet: this small ram seems to be more robust and it was probably used for almost front-attacks tending to destabilise the enemy ship. Radiographies of this ram have not found any indication of welding "consequently this artifact was integrally casted into the sand", following the method of the lost wax. In conclusion, this is a high quality achievement of the ancient Greek Technology.
Besides, the solid wedging of the ram to the keel, seems to be a remarkably demanding work. Into the hollow space of the rear part of the ram one should insert the ends of the first timbers of the ship, in such a way that the shock energy to be distributed to the maximum possible mass of the hull. Murray is very instructive in showing a replica (Fig. 28) of a ram he fabricated in collaboration with K. Zachos: Instead of the timbers of the prow, marbles are inserted in the rear part of the ram - the marbles of the Nikopolis Monument in which the architects of Octavius had "fitted" 36 rams from the captured ships of Cleopatra and Antonios (sea battle of Action, 31 BCE). This was the ignominious end to the shipbuilding history of the Hellenistic World...
However, this had been preceded by another 'excessive' use of rams by the Ptolemies. Around 210 BCE, when Ptolemy IV Philopator built a gigantic, 130m long twin-hull ship ("with two prows and two sterns"), he equipped it with "seven rams, one of which was longer than all the rest, and the others were of smaller size; and some of them were fixed to the ears of the ship" [Athenaeus, E.204a]. The "ears" were strong beams fitted transversely near the stern, jutting outside the hull and reinforced against impact. We have no convincing evidence of the dynamic strength of such a layout, nor of the capacity of a ship like that to sail off.
- Finally, let us add here a rare historical event which demonstrates in another way a broader significance of the rams of warships: In the late 4th c. BCE, while the Carthaginians had prevailed over almost the whole of Sicily, Agathocles, the tyrant of Syracuse boldly ventured to Libya, burned his entire fleet so that his army would not entertain any defeatist ideas, conquered two hundred towns and mounted a siege against Carthage (at the same time as the Carthaginians laid siege to Syracuse!). And this is what Carthaginians did as a diversion: they collected the rams of the 'self-burnt' Greek fleet and sent them to Syracuse as 'evidence' of the supposed annihilation of Agathocles, so that the city would surrender itself in despair. The ruse may have not worked, but here is how the unburned bronze rams were turned into 'substitutes' for a siege on land [Diodorus, 7.3/9.2/15.2].
Tassios T. P., On Technology In Ancient Greece, 2018 Angelakis, Athens