In 1160 BC T71, I open borders with Brennus and get his trade routes, though my map has no city of his. He has a city on the west coast, 4 tiles north of the gem; I know Sailing and have a coastal trade route to this city.
I fail to notice in T71 that Brennus has already connected ivory. The 2 ivory on my map are outside his borders, but he has 2 other ivory. I meet Brennus in 950 BC T77. He refuses to give his spare ivory because, "We just don't like you enough." I give a fish (for nothing), but get no diplomatic boost, because Brennus soon connects his own fish. My Warrior maps Brennus's civ, and some empty land to his north; my Warrior survives a barb Archer but dies to a barb Warrior. Brennus has better land than me; he has horse, iron, and ivory; I fear that his War Elephants would crush my Axemen in a war.
Brennus's missionary spreads Buddhism to Koe in T83, and I immediately convert to Buddhism, 1 turn before I settle
Koper "copper" (my 5th city, 775 BC T84). Someone finishes the Oracle after I end my turn T86. I enter the classical era with Metal Casting in T87, then learn Mathematics in T95. Brennus annexes the last ivory, but I run a Settler across the jungle, and settle
Six North (my 6th city, 400 BC T99).
The new city is exactly 6 tiles north of my capital, and will steal the ivory in its 1st ring. (This ivory is in the 3rd ring of Brennus's Vienne.) Brennus misses his chance to declare war, steal my Workers near Six North, and deny ivory. Six North builds Granary, Library, Walls.
I fail the Colossus before I begin it. I would have begun the Colossus in T100 (which is 13 turns after I got Metal Casting), but someone completes the Colossus after I end T99, so I never get any gold for failing it. (I later get 165 gold for failing the Pyramids.) The Colossus needs a Forge in a coastal city. Vuurtoren completes my 1st Forge, but has no forests. I wait until I learn Math (to boost forest chops), then chop forests at Koper to complete my 2nd Forge in T100. This is too slow. Koper had wasted hammers on a Granary before its Forge.
I learn Alphabet in 300 BC T103 and expect to trade techs with Brennus, but he refuses, "We don't want to start trading away this technology just yet." Brennus has Hunting, Iron Working, and the techs before Monarchy. I decide to run for Monarchy, because my cities are unhappy. I research Mysticism, Polytheism, and Monarchy, then revolt in 50 BC T113 to adopt Organized Religion and Hereditary Rule (after 1 turn of anarchy). Because I don't know Hunting, I can quickly build Warriors (not Spearmen), who happify my cities.
I learn Iron Working in T119, and discover that I don't have iron. I also don't have horse, but do have ivory by Six North. I now want to use my ivory to build War Elephants to conquer Brennus's land and resources. Also in T119, Brennus and I race Settlers toward the gem on the west coast. In T120, Brennus's Settler is on the gem, but I have a road to the gem, so I move my Settler to the gem and immediately settle Gold Medal (my 7th city, 125 AD T120). I win the race by half a turn!
The gem under Gold Medal becomes my 1st happy resource. The city will reach a fish and a rice, and needed Iron Working to remove the jungle from the rice. I research Currency for its trade route, then Construction, Horseback Riding, and Hunting, so I can attack Brennus with War Elephants and Catapults. After I end my turn 325 AD T128, I get my national
Moai Statues in Corneria, adding hammers to its water tiles.
Brennus becomes Friendly, because I had adopted his religion (Buddhism) and his favorite civic (Organized Religion). Friendly Brennus can trade techs, and I want his Code of Laws, so I give my 2 techs (Metal Casting, Alphabet) for his 4 techs (Code of Laws, Meditation, Priesthood, Archery).
I research Machinery, Compass, then Optics in 800 AD T150. I find T151 Suleiman, T152 Hatshepsut, T161 Tokugawa, T163 Zara Yaqob, T164 Cyrus. In T169,
"Your maps prove that the world is round! You receive a +1 ship movement bonus."
840 AD T152 is the big turn, as I convert to no state religion, then
declare war on Brennus. My western stack of 5 War Elephants and 2 Catapults departs Gold Medal and captures a Worker. My eastern stack of 4 War Elephants and 6 Catapults departs Six North. This war is risky, because Brennus has the larger civ (he has 9 cities; I have 7), a tech advantage (Feudalism for Longbows, and later Guilds for Knights), and a resource advantage (horse and iron). Brennus began the war with a small army and too few War Elephants; I unplugged his last ivory in T170. My western army conquers
Tolosa in 1000 AD T160.
My eastern army gets stuck outside Vienne. Brennus surprises me with a stack of 1 Knight, 3 War Elephants, and 3 Catapults, who retake Tolosa in 1330 AD T173. He also slays most my units by Vienne. I reply by conquering
Camulodunum in 1150 AD T175, on the west coast north of Tolosa. Brennus retakes Camulodunum in 1300 AD T190, then reconnects ivory.
I had researched Machinery, Compass, Optics, Engineering, Aesthetics, Literature; built the Heroic Epic in Corneria; built Trebuchets and more War Elephants; and acquired 2 Great Generals, who promoted 2 Spearmen to Medic III. As Brennus retakes Camulodunum, I move the western army of El Cid toward Tolosa, and the eastern army of Auitzotl toward Vienne. Brennus sacrifices Catapults to slay Auitzotl and most of my eastern army. El Cid's army takes Tolosa in 1350 AD T195, but Brennus also slays El Cid and retakes Tolosa in 1380 AD T198. I have lost all my conquests.
My stats in T199 show big losses: 29 of 36 War Elephants, 16 of 17 Catapults, and 8 of 15 Trebuchets; but only 1 of 24 Axemen. So why do I have so many Axemen? My cities became unhappy, and I have Hereditary Rule, so I built more Axemen to happify my angry citizens. This was a mistake, because I wasted too many hammers on Axemen. It would be cheaper to build Archers; but I also have Slavery, so it might be better to whip away my angry citizens to build more War Elephants and siege units to attack Brennus, while keeping fewer defending units in cities where Brennus can't reach. My other mistake was to advance north from Tolosa to Camulodunum. Tolosa wasn't safe, because Brennus can easily attack Tolosa from Bibracte, his capital and Buddhist holy city.
I will rewind the game from T199 to T151 by loading an old save. I have the option to stay at peace, but I might redo this war.