In the Beta version, there's sea walls and sea towers. But they were taken out when the game showed up in stores. However people got around the beta limit by playing AOE scenarios in ROR, and some weird results turned up, stuff like blacksmith being only placeable on water, some ships that work like monks(boards(convert) other ships), A new type of gaia others item - The spear sticking out of grounds, new units such as infiltrator, berserker, Heavy Swordsmen(looks same as broad swordsman in aoe), halberdman(were converted to halberdier in TC). Sea gates and sea walls were one of those weird units.
You can make sea gates using sea walls. simply use the "tower gate" trick on a regular stone gate, but use medium or deep water this time since sea walls were not placeable in shallow water. Afterward simply add in the walls.
You can use the same result on a sea gate, use water to delete the gate part and that left you 2 sea walls.
And yes, Sea gates and Sea walls are in EO's New Units and Objects Template
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