I just replayed the same Emperor-level normal-size marathon-game 3-4 times, just because it was so much fun in exploring how the AI engage in large-scale warfare. By building up my own military in different ways and starting the war in different ways, the AI (Augustus) responded with different build queues.
In one iteration, the war was mainly naval and we fought over 2 oceans, each with 2 vassals. By the time the naval war was decided, the land war was almost anti-climatic.
In another iteration, I wiped out one of the other civs to control more land/ports, so I only had 1 vassal while he had two. It was a mainly land war as I forced a landing with the first move of the war with 25 Transports landing 95 units (lost 5 on amphib assault) and we fought it out on land. Before the end of the land war, the more powerful of his vassal abandoned him and negotiated a separate peace.
In yet another iteration, the initial landing wasn't with the same force, and it became a running sea battle as I tried to keep the sea lanes open while Augustus tried to sneak in convoys and nuke-armed subs.
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For the land-battle version, the final count of "modern" units lost/killed was
Lost by me (Maya)
17 Tanks
53 Modern Armor
34 Infantry
48 Mechanized Infantry
35 Gunships
Very little in the way of SAM and mobile artillery units lost, and I'm not counting air.
Augustus and his allies lost
56 Tanks
165 Modern Armor
133 Infantry
193 Mechanized Infantry
174 Gunships
39 Mobile SAM
36 Marine
80 Paratroopers
17 Navy Seals
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As you can see from the kill ratio, the win hinged on making sure that I attack only when advantageous, and taking advantage of terrain/promotions. In the land-war version, the Demographics showed the Romans with over 14 million soldiers to my 7.4 million.
The key to victory is always to invite the AI to attack you, and then coop them up in their cities so that you can bring the advantages of a City-Raider promoted Modern Armor to bear.
Boatloads of fun...