The Gupta Empire ruled northern India from 320 to 647 CE. Key Gupta rulers included Chandragupta I and Chandragupta II, who expanded the empire and engaged in profitable trade with the Mediterranean world. A Chinese monk described people in India during this time as happy and charitable, though the caste system was becoming entrenched. The Guptas achieved advancements in art, medicine, mathematics, literature, astronomy, and other fields. However, invasions by the Huns in the 4th century began the decline of the powerful Gupta Empire.