Hannibal left in June 218 BC Cartagena (Spain), to attack Rome from the north. He hoped to relieve the endangered Carthage.
In November he arrived at the Alps.
With 38.000 footmen and more then 8.000 horsemen Hannibal departed from the Rhône river.
15 days later he arrived on the plains of the river Po with only 14.000 soldiers and 6.000 horsemen, but all of the 37 elephants.

The Great St.Bernhard-Pass connects the Rhône river valley at Martigny in the north with the Dora Baltea valley at Aosta in the south. 
The soil for this project was collected on both sides of the Pass at constant heights. 
The difference in height between the collection points represents two Roman "stages" (a Roman unit of measurement).

Hannibal most likely travelled from the Rhône river through the Arc valley over the Col du Clappier 2477 m, and reached the capital of the Taurians, the city of today's Turin in Italy.

The History

814  BC
Founding of Carthage
c. 425
Hanno travels to the west coast of Africa and Himilko to the coast of Brittany.
264
The first Punic War begins.
247
Hamilkar Barca takes command of the Carthaginian forces in Sicily. Hannibal is born.
244
Hamilkar besieges Monte Eryx in western Sicily.
242
Roman victory over the Carthaginian Navy.
241
The end of the First Punic War.
240
Revolt amongst Carthaginian mercenaries.
237
Hamilkar crushes Carthaginian mercenary revolt.
237 - 236
Hamilkar and his son Hannibal leave North Africa on their way to Spain. At departure, Hannibal swears "never to be a friend to the Romans".
235 - 230
The Carthaginians expand their power base with their conquest of Spain.
231
Founding of Cartage Nova (Carthagena) trough Hasdrubal.
230
Death of Hamilkar. His brother-in-law Hasdrubal takes command of the Carthaginian forces in Spain.
226
Hasdrubal and Rome agree on the boundaries of areas over which they rule; the Carthaginian Empire ends at the south shore of the Ebro.
221 
Hasdrubal is murdered. Hannibal becomes the new commander.
219
Hannibal conquers Saguntum.
218 
Outbreak of the second Punic War. Hannibal departs in June from Carthagena, Spain with 90,000 soldiers and 12,000 riders. After the crossing of the Pyrenees, 50,000 men and 9,000     riders remain. He reaches the Alps in November. He departs the Rhone river with 38,000 men on foot and 8,000 riders. With only 14,000 men and 6,000 cavalry remaining, but all 37 elephants, he reaches the river Po after 15 days. Before the end of the year, he conquers the Roman army under the command of Scipio d.A. at the Trebia River.
217
Almost blind, Hannibal leads his troops on the last elephant "Surus" through the marshes along the Arno. Later, he destroys the army of consul Flaminius at the Trasimenian Lake, shortly thereafter, the cavalry of the consul Servilius. Rome is now defenceless and a dictatorship is formed under Quintus Fabius Maximus.
216
With 40,000 foot soldiers and 10,000 cavalry, Hannibal crushes the Romans under the consul Servilius and Atilius, who had stood for battle at Cannae with 80,000 men and 6,000 riders. The Romans lose more than 70,000 fighters, which are more soldiers, than the Royal Air Force lost during World War I and II combined. Many allies in the southern part of the country break with Rome. Hannibal erects his headquarters in Capua.
215
The Roman treasury is bankrupt. Hiero of Syracuse dies. Heir to the throne is Hieronymus. Syracuse rises up against Rome.
214
Hieronymus is murdered. Riots break out in Sicily.
213
Marcellus plunders Leontini and besieges Syracuse. Tarentum takes sides with Hannibal.
212
Marcellus conquers Syracuse. Archimedes is killed. Hannibal defeats the Romans in Apulia.
211
Hannibal marches on Rome. Capua surrenders to the Roman troops.
210
Again the Romans are defeated in Apulia. They are victorious in putting down the unrests in Sicily.
209
Fabius conquers Tarentum back. 12 Latin colonies oppose any further war service.
208
Scipio defeats Hannibal`s brother in Spain. Hasdrubal crosses the Pyrenees and reaches the transalpine Gallia.
207
Hasdrubal crosses the Alps and reaches the zisalpine Gallia. Scipio defeats the last Carthaginian army in Spain. Hasdrubal is killed in action in the lost battle at the Metaurus.
206
Hannibal`s youngest brother Mago leaves Spain and sails to the Balearean Isles. The war in Spain comes to an end.
205
Mago lands in Liguria and conquers Genoa and Savona.
204
Scipio reaches land in North Africa with his army.
203
Hannibal leaves Italy for the last time. For 16 years, he has remained in the land of his enemy. During this time, Rome sent a     total of 750.000 troops to fight him.
202
Hannibal is defeated by Scipio (Africanus) in the battle at Zama. End of the second Punic War.
201
The Romans and Carthaginians sign a peace treaty.
200
Hannibal becomes chairman (Sufet) of the Magistrate in Carthage. He reorganizes the economy and the money market and succeeds in the recovery of the political system despite considerable reparation payments to Rome. He is top statesman for five years. 
195
The privilege-less nobility of Carthage betrays Hannibal to Rome, who flees to Tyrus, the old capital of the Phoenicians and founding city of Carthage, and offers his services to the Seleukide kingdom.
197
Philipp of Macedonia is defeated by Rome.
183
Hannibal kills himself in his last exile, Bithynia, in order to avoid his capture and execution in Rome.
149 - 146 
Third Punic War.
146
Destruction of Carthage

Hannibal represented the only threat to Rome`s vision of its empire through to its fall.