The Magic Yellow Stone - book six - Tom with Francis Drake.

The series "The magic yellow stone" tells the story of a 16 years old English named Tom, who had found a magic yellow stone on the ground where he took a sleep, while being om tour to Rome, Italy with his Parents and his sister Helen 15 years old.
Taking the yellow stone from the ground and cleaning it caused a sudden strong wind to take him to the past.
The first place where he was reached was the Alps mountains where he met with Hannibal and his army crossing the mountains on their way to fight the Romans.
Tom quickly had to fight Barbarian tribes trying to prevent the Carthaginians to cross the Alps.
Tom distinguish himself and became a high cavalry commander, participating in all Hannibal battles against the Romans.
The series describes other places where Tom reaches after cleaning the Magic yellow stone,
Vasco da Gama, Francis Drake Alexander the Great, Darius the Great and many more famous men from the past,
Till now the series has 21 books.