Why Did The Prophet Marry `A’ishah at Such a Young Age?

Why did the Prophet (peace be upon him) marry `Aishah (may Allah be pleased with her) at such a young age?

The Prophet (peace be upon him) married his wife, `A’ishah, at a young age. Nowadays, getting married at such an age is seen from a different perspective. What was the reason for the Prophet marrying `A’ishah at a young age?