Duncan Head and I wrote a timeline on the old board where Carthage defeats Rome and stuff happens.
The POD is an immediate attack on Rome after the near-annihilation of the Roman Army at Cannae. Geographically this might be extremely tricky to pull off.
The Timeline
216 BC-Carthaginians lay the proverbial smackdown on the Romans as OTL. However, they immediately follow with a forced-march to hit Rome itself before the preparations can be made for a siege.
216 BC (some time later)-The Carthaginian army hits Rome after the messengers telling of Cannae. Some siege preparations are made, so they simply can't immediately occupy the city.
215 BC-Bolstered by reinforcements from Capua and other Italian cities dissatisfied with Roman dominance, the Carthaginians take Rome by storm. The city takes awhile to fall in nasty house-to-house fighting and Rome is ultimately burnt to the ground after much rape, pillage, etc.
215 BC (a few days later)-Capua proclaims the "Confederacy of Italia" with much autonomy for every city (so a dominant center like Rome doesn't arise).
215-20 BC-Hannibal returns to Carthage and continues his OTL reforming policy. He remembers his father's experience after the First Roman War and decides to lessen Carthage's reliance on mercenaries by creating a professional army which only Carthaginian citizens can join. The on-hand mercenary units from the Second Roman War are used to finish up with Spain (and hopefully reduce their #s so they're not a threat...sort of like what happened with the Samurai in the "Composite ATL"). The mercenary conquest is generally brutal and there is much oppression.
70BC: Ariovistus leads a coalition of Suevi and other German tribes across the Rhine into Gaul.
60BC: Ariovistus falls out with his former allies the Aedui, one of the dominant Gallic tribes. He defeats them and they call for help from the Carthaginians with whom they, in turn, are nominally allied. Bomilcar, the governor of Carthage's small Gallic province (centred on Massilia) leads an army north but is defeated and killed by the Germans. This is usually taken as marking the beginning of the age of migrations.
59-58BC: Pressed by the Germans, the Helvetii migrate from Switzerland to Aquitania. The displaced Aquitani in turn invade Punic Spain. They devastate the north of the country but are eventually wiped out.
4 BC-Jesus born to Mary in Bethlehem, sort of as in OTL (owing to the different political situation, perhaps there will be room at the inn or some other changes).
3 BC-Political instability leads to a Parthian incursion in support of Herod the Great, an Idumaean claimant to the throne of Judah against an Egypt-backed Hasmonean coup. Mary, Joseph, and the baby Jesus flee to Egypt to escape the mayhem; the cruel Parthian commander orders the killing of all male children in Bethlehem after a unit of pro-Hasmonean militia raised in Bethlehem kills one of his key commanders (he doesn't want another generation of Bethlehem-ian men).
1 AD-Jesus and family return to Bethlehem (complete with Jesus's half-brother James). Christ's life goes as OTL pretty much.
33 AD-After offending the priests yet again, a mob (instigated by the priests) drags Christ to the Well of Bethseda, where He had recently healed a cripple, and drown him. They then cut up his hands and feet with knives in their frenzy. However, a dissident priest takes pity on Christ and buries Him in his newly-made tomb. According to Christ's followers, He rose from the dead 3 days later.
40 AD St Thaddeus brings Christianity from Egypt to the Carthaginian domains. He and his companions are traditionally portrayed as journeying along the Libyan coast on camel-back. While St Thaddeus did not historically introduce the camel himself, its spread at roughly the same time as the spread of Christianity leads to the two being linked in popular thought.
190 AD-The Goths begin migrating south and west into the lands north of the Black Sea and put pressure on some German tribes further west, who in turn put pressure on other German tribes, etc.
195 AD-The leaders of the Franks, Vandals, Angles, Saxons, and other lesser Germanic tribes convene, elect a renegade Gothic chieftain named Eberwolf as their king, and decide to move West. Their confederation takes the name of the Wandrin (wanderers).
200 AD-Accalon, a visionary chief of a small Celtic tribe in Gaul, sees Gaul's frontiers being steadily eroded by the Germans. He begins unifying the Celtic peoples to resist the Wandrin influx, a process that will take some time.
202 AD-Accalon proclaimed High King at Vesontio (present-day Basancon) after the defeat of several German-backed Celtic chiefs and begins preparations to expel the invaders from Gaul.
204 AD-Accalon begins his campaign to "cleanse" Gaul of the Wandrin invaders. He leads an army of Celtic people against the Germans, who've conquered all the way to the Meuse and upper Seine, forcibly assimilating the Nervii, Aduatuci, and Treveri Celtic tribes.
205 AD-Stung by a series of Celtic victories, Eberwolf marshals his forces and meets Accalon head-on at the source of the Rhone river in the territory of the Lingones tribe. Though Eberwolf is killed in single combat with Accalon, the enraged Wandrins carry the day and nearly obliterate the Celtic army. Accalon rallies the survivors and they flee to the lands of the Carnutes (between the Loire and the Seine) to marshal a new army. The Celtic peoples of the northern region are evacuated southward towards the Garonne River. The Franks and Saxons are settled in the area as a reward for their service by Eberwolf's son Winguric.
207-A two-pronged German offensive encircles the Celtic army at its base in the Carnutes' tribal area. The Celts managed to escape, but not before losing half their army. Accalon, grievously wounded in the battle, realizes that there simply aren't enough men in Gaul to raise a new army and that the war is essentially lost. Though barely able to walk due to his injuries, he leads the remaining Celts of Gaul into northern Spain.
207-Battle of the Spanish Marches. Commanded by a notorious cruel and decadent Carthaginian, Spanish conscripts are massacred by the battled-hardened Celtic armies. The Carthaginian commander, captured as he tried to flee (he ordered his troops and officers he didn't like in one direction and he and some of his favorites--in more ways than one--went in the opposite), is kicked to death by Spanish prisoners. The canny Accalon proclaims the end of "Aethiopian despotism" and the eventual liberation of Spain. However, owing to the losses from the wars in Gaul and the Battle of the Spanish marches, he has to settle down and replenish the ranks through more Celtic children and the recruitment of all-too-happy Spaniards. The Celts occupy the northern 1/3 of Spain, while continuing to raid the Wandrin who've moved further south almost to the Pyrenees.
208-The Carthaginian government raises taxes so high that fully 60% of the non-Punic population ends up as serfs. A huge percentage of these serfs are then conscripted to be used as cannon (sword?) fodder. Tacfrinas, a Berber chief who's skirmished with the Punic leadership over the taxes his nomadic people have to pay, is troubled, but cannot think of what to do besides killing tax collectors/impressors and fleeing the inevitable wrath into the deeper desert.
209-Massive Carthaginian offensive into northern Spain. It fails badly as at least 1/3 of the troops defect to Accalon, 1/3 desert, and 1/3 are obliterated. One of the dead is Tacfrinas's firstborn son, who was captured during a skirmish between Tacfrinas's tribe and the central gov't.
210-Shaken by all this, Tacrfrinas contemplates suicide, but a wandering friar persuades him to become a Christian. The idea hits on Tacrfrinas to use the new faith, which is spreading throughout the oppressed lower classes and even a few dissident Punic people, to destroy the cruel Carthaginian overlords.
210-11 AD-Tacfrinas's revolt. Berber riders bearing the flame of revolution ride throughout northern Africa, causing the people to rise up against the conscription, taxation, and casual cruelty of the Punic overlords. Punic Spain is wracked by revolution, but the utterly homicidal governor crushes it with hostage taking, public blood offerings to Moloch, and other doings. However, Carthage itself is taken by storm and destroyed amid brutal "frontier justice" for most of the Punic aristocrats in the capital (despite Tacfrinas's appeals for calm). The center of government is moved to Tunis and serfdom is abolished, though conscription will remain until the end of the "emergency."
212 AD-Tacfrinas dies from a scorpion sting as he prepares to lead the army across into Spain to deal with the Punic governor, who is marshalling an army of Punic peoples and mercenaries (he doesn't trust the Spanish now at all) to attempt to defeat Tacfrinas and retake Northern Africa. Tacfrinas's son decides against taking the war to Spain, but fights defensively and defeats the Punic couter-invasion.
213 AD-His army bolstered by the oppressed Spanish, Accalon see his chance and pounces on the Punic governor, destroying the remnants of his army and giving the governor himself over to his Spanish allies (where he is promptly torn to pieces, literally). The Tunisian military hops over the Straits and seizes a few outposts in southern Spain as a means of "saving face" and setting up a buffer against the Celts. Accalon, content with 90% of Spain, does nothing.
215 AD Tacfarinas's successors institute a state Christian church, bans public pagan worship and all forms of human or animal sacrifice. This "Koinon of St Thaddeus" (I don't know a suitable Punic or Berber term for a league or federation, so I'll go with the Greek, we've had enough centuries of Hellenistic civilisation for it to be plausible) is a federation of tribes and cities in Africa and the remaining Punic outposts in Sicily, some of the other islands, and a few coastal parts of Spain. It never establishes an effective central government, though Tunis retains great prestige as the spiritual centre, seat of the head of the Western Church.
c.250-300 Doctrinal civil wars split the koinon. (Probably this TL's equivalent of the Donatists: Africa was a bit of a hotbed of heresy in OTL.) Barbarian raids increase. Italian Celts take Sicily, Spanish Celts take all remaining Tunisian outposts except the Rock of Melqart (Gibraltar). An Italian Celtic naval raid sacks Utica, and Tunis is only saved in a brilliant counter-attack by the aristocratic Numidian general Jacob Masinissa, leading a semi-private army, many of the troops levied from his own estates or his fellow-tribesmen. A grateful Patriarch of Tunis is persuaded to appoint him First Shophet, that is chief magistrate of the Koinon. After further successes against barbarians and dissident cities, he establishes a firm centralised state over OTL Tunis and eastern Algeria, and is appointed First Shophet for life.
c.300-400 The Masinissan dynasty become hereditary Shophets, at first ruling in co-operation with the Council and the Church, and reconquer most of former Carthaginian Africa, from Morocco to Tripoli. Conspirators wishing to "restore the liberty of the Koinon", backed by Egypt (currently ruled by a Mamluk-style military regime set up by its Arabian mercenaries, and fearing a Tunisian attack on Cyrenaica, which has been quietly absorbed by Egypt during the decades of chaos), start a civil war. After defeating them, Judah II Masinissa is proclaimed Emperor of Tunis and crowned by the Patriarch.
1100 Cuman Khan Boniak defeats Khaqan Igor of the Rus outside Kiev. The city is sacked, and the Rus khaqanate reduced to a group of Cuman vassal-states. The north (OTL's Novgorod) moves back into the orbit of the Scandiavians.
1180-1220 The Kereits under Toghoril Khan unite the steppes north of China, defeating and absorbing rival coalitions including the Tatars and Monggols. The triumph of the Turkic-speaking Kereits leads to the disappearance of the Mongolian language-group. The Kereits win out because they have a greater sense of unity, coming from a national religion: I did think of this being Christianity (Nestorianism was influential in Mongolia in OTL, so it wouldn't take much change to have a version of Christianity being stronger there in TTL). However they could alternatively have picked up militant Mithraism from Persia.
1230-50 Kereit armies move West, overrunning Central Asia. They destroy Volga Bulgharia and the Cuman confederation. The Rus become Kereit vassals.
1260-80 Devastating Kereit raids into Eastern Europe. Cuman refugees establish a state along the Danube.
1300 Hannibal IV Thiudarik, king of the Asdings, defeats the Kereits on the Oder and begins the Gothic expansion eastwards.