Sparta's borders expanded (from the Oracle) to activate the pigs for Thermopylae. Thermopylae got religion by itself shortly, which would push the border for the gems. We also turned out to have Horses at that city, very helpfully. Sparta built a work boat and Athens a galley to go poke around and see what there was to be seen before caravels.
Now I tried to plan out something else: a beeline to Optics and Astronomy, which also goes through Machinery for macemen. And I spent about an hour poring over the Great People Tech Preferences list to figure out the best way to use GPs to lightbulb towards that end. The best I could do was use a Great Merchant now to lightbulb Metal Casting. An Engineer to lightbulb Machinery would be awesome, but the problem there is that Engineer points come too slowly (Caste System doesn't help), and neither city could have a pure Engineer gene pool. Prophets and Artists were useless for that tech line. Finally, a Scientist would not help because Philosophy was in the way and couldn't be blocked. A second Scientist could lightbulb Optics, though; we'll decide a bit later if that's worthwhile.
So along with the Bureaucracy civic swap, I went to Caste System for the express purpose of hiring two Merchants in Sparta. This would give me a 66% chance of a Merchant next (competing with the Oracle); I'd bump it up to three merchants at a food deficit slightly later to get that percentage up to about 70%.
While waiting for the Great Merchant, I filled in Bronze Working, Pottery, and Animal Husbandry, then went for Iron Working. The RNG behaved well, and delivered me Harkuf on schedule. I kept going with the plan of getting two Great Scientists next to lightbulb Philosophy and Optics, the latter of which required me researching Machinery and Mathematics. So I kept running max scientists in both Athens and Sparta.
Presently my exploring work boat and galley started making contacts, though with tech trading off and diplomatic attitudes irrelevant with a conquest game plan, there really wasn't anything to do diplomatically.
Unfortunately, the RNG balked on the next Great Person from Sparta, delivering me a 30% odds Prophet instead of the 70% Scientist.
I didn't want the Confucian shrine as I had no plans to bother spreading the religion and didn't want more Prophet pollution in the GP gene pool. But this Prophet would actually be fairly useful to lightbulb into Theocracy, as now I was planning to go to war pretty much as soon as Macemen arrived. And now, it wasn't worth trying to spend two further Great Scientists to lightbulb Optics which really isn't all that expensive.
I shut off the specialists in Sparta, and ran the scientists in Athens just a little while longer to cash out on those GPPs with one more GSci to settle in Athens, multiplicative with the Academy there.
So I paused Machinery to research Polytheism-Monotheism, then lightbulbed Theology (founding Christianity) as that last GSci came from Athens. Since Caste System was no longer needed, I took this chance to double-revolt to Theology and Slavery.
I'd been beelining Optics in hopes of getting circumnavigation with caravels, but something surprised me. That work boat and galley, exploring in opposite directions, just somehow never ran out of islands to explore. They kept pressing onwards, and suddenly sighted each other on the far side of the world.
Circumnavigation!
So I was building up for a maceman war against my nearest neighbor, Russia. 
I realized there was a galley route to Moscow -- as long as we kept our open borders active. I'd have to sail through that one ocean tile in Russian territory, then out to the neutral territory south of Russia, then declare war, then make my landing. This also meant that there would be no reinforcing once Moscow was razed! My initial fleet had to take along everything I needed. That meant four galleys carrying all this: one phalanx, five macemen, a settler, and a worker.
Unfortunately, Catherine surprised me by canceling our Open Borders! Fortunately, I poked around more and discovered that there was still a coastal route to Moscow a bit farther west, though a bit more roundabout.
And here we go. Well, before we declare war, let's take a look at some of the statistics.
Surprisingly, my GNP isn't even tops, despite the CS slingshot. Well, that's because I don't have a lot of cottages at the capital to power up Bureaucracy. This graph tells more of the story, that my hammer production is half again as high as anyone else's.
And what happened to the hammer production of Catherine, my immediate target? Her entire civ is producing about six hammers. 
This was strange enough that, after finishing the game, I went back to the 600 AD save and looked at the city (by putting a Spy for the player in the city via Worldbuilder.)
Oh dear. 
The poor thing got its city stuck WAY over the health cap into starvation territory, so it had to work only food-producing tiles with no shields. I think this happened because it cut down forests; in an earlier save from 1000 BC, Moscow had four forests for +2 health. At least the AI correctly built an aqueduct to deal with the problem. But why didn't it WHIP the bloody thing, since the population would starve anyway? Russia was in Slavery, and Moscow had no recent whip anger. 
Back to the present, here's the current demographics:
Since when does the human have a population half that of his best rival, on Prince difficulty? Well, some of that deficiency was due to whipping macemen. But I'm betting that somebody else just has a lot more land to work with. We'll fix that in time, as we go a-conquering.