I like the idea of turret points on boats. I think it would go well with #8957. In my opinion we also need some logic to allow shrinking turetable unit model's => When a unit is turreted on a boat, it become 20% smaller. Just for visual consistency with boats being a bit smaller then they should. Also as you pointed out, units should die when the boat sinks.

Maybe after being placed beside a wall, units could go slowly up, in the same way they go up when they are posted on top of walls. Would look a bit goofy right now, but still.   Yes, the Assyrians would do that to ram a thinner part of the walls. In this case, Old Smyrna 1948-1951 by J. M. Cook states that "so gigantic a mound, raised from the low ground to overtop the city fortifications, can only be explained as a siegework; and on chronological grounds therefore it can with certainty be attributed to Alyattes", which would seem to imply that they built it all the way up for troops to climb, but then it says "at a low level in the mound (about 8 metres above sea-level) a large mass of solid mud brick was encountered in our excavation; this may possibly have fallen from a breach effected in the superstructure of the city", and later on "the mud brick superstructure of the fortification there fell forward at the time of the capture or very soon after", which seems to imply ramming at a higher level. Maybe "overtop" was not literal, and the second interpretation (the Assyrian way) is indeed the faster way to do things. All this is a bit of a problem since I don't think troops carrying a log (even capped with metal) would have had enough strength to break a wall, even at a higher level. Interestingly enough, this was also the case for the Thucydides quote already mentioned, before stating the "snapped off the nose of the battering ram" bit, he says that "while raising the mound the Peloponnesians also brought up engines against the city, one of which was brought up upon the mound against the great building and shook down a good piece of it", thus, these were already engines, used in the Assyrian way. All this means that I don't see these siege ramps/mounds viable before having proper battering rams, which coincides with both appearing in Greece in the 5th c. BC, as mentioned before.   I think the earliest attestations for these in Greece come from the 5th c. BC.   In conclusion, and besides the guys with a log (after all, D. B. Campbell in Greek and Roman Siege Machinery 399 BC-AD 363 states that "it is very likely that Western warriors would soon have discovered the value of a stout tree trunk in bursting open a gate"), what seems reasonable in chronological order is: spies, climbing mud-brick walls at certain points, at some point capping the log with metal, after that (EDIT: or before, who knows exactly, both could be independent in the game) and seemingly before the 5th c. BC building a non-movable shed for it, and having ladders for the newer unclimbable stone walls.

I don't have time these days to investigate it, but the first thing I would do is follow @Stan` advice and study how it's implemented in the garrison 

The ramps and ladders are interesting but would be somewhat difficult to animate, hence the idea of making it a passive bonus or tech (i think siege ladders are already a technology, or at least they are in the DE mod). One interesting tidbit about earthen ramps is that the famous Assyrian towered rams were apparently mainly used on top of such ramps to damage the enemy battlements. Does this mean the Lydian ramp was meant for rams? perhaps but there is no definitive proof (Rams built in the "Hurrian manner" are already mentioned in Ḫattušili I's siege of Urshu so they might not be entirely new to Anatolia) This is a quite interesting siege method for civilizations without heavier siege equipment; again a bit dificult to implement (and i'm not sure how much it was used in archaic period itself). Although perhaps it would be possible to implement a simpler ''underminer'' unit that attacks enemy walls with the villager's pickaxe.

Indeed, surely this started early. For the ram I mentioned, Thucydides states that the defenders "snapped off the nose of the battering ram", implying it was capped, probably with metal like the Olympia ram, which is from around the same period. There are plenty of engagements for which there are no records, but in any case, attacks were usually concentrated on the gates.   I don't see that as desirable, but other possibilities could be: -Spy units hard to see to the enemy, which I proposed recently, could open gates. This is not some far fetched Trojan Horse thing: "political factions aiming at the overthrow of a government could render invaluable assistance in several ways. One method was the opening of the gates of a city under siege. Another was to make it possible for enemy forces to enter the besieged city under the cover of darkness. An excellent example of this is provided by the siege of Plataiai. According to Thoukydides (2.2.1-3), a force of three hundred Boiotians entered the city at night with the aid of Nauklides and his friends who opened the gates for them", from Espionage and Treason in Classical Greece, by A. Gerolymatos. -Later on, siege ladders could be considered, since apparently they "are mentioned in a fragment attributed to Archilochus" ca. 650 BC. -Even later, around 585 BC "the Lydians, presumably under Alyattes II, took Old Smyrna by building an earthen siege ramp" (which included wood). Maybe the Greeks learned from that, but their use by them is not attested until over a century later. -On top of all that, initially walls would have been made mostly of mud-brick, which "resting on a low rubble socle, was not very high or very strong", from Ancient Greek Fortifications, 500-300 BC, by N. Fields. This would have made "climbing the stone and mubrick walls" feasible at some points (as mentioned in the Iliad), where their slope wasn't as steep. For game purposes these points could be where the walls take a turn, and some units could be able to walk over them (at a great speed and resistance cost). In any case, at some point "all-stone fortifications became more common", allowing for taller and steeper walls. Still, there's an interesting difference between both kinds of materials, although maybe hard to implement in the game: "against the blows of engines brick brings greater security than fortifications built of stone. For stones break and are dislodged from their fittings; brick however, does not suffer so much from engines, but it crumbles under the action of water just as wax is melted by the sun" (the last method being how Sparta took Mantineia).