Final answer:
Alexandria in Hellenistic Egypt was a key site of cultural and commercial encounter, known for its Museon, the great Alexandrian Library, and its significant population diversity.
Step-by-step explanation:
The city that became an important site of encounter in Hellenistic Egypt was Alexandria. Founded by Alexander the Great in 331 BCE, Alexandria was the capital of the Ptolemaic kingdom and became the largest city in the Hellenistic world. The city was known for its significant cultural contributions, including the Museon, also known as the home of the Muses, and the famous Alexandrian Library, which housed the most extensive collection of books in the ancient world. Furthermore, Alexandria's strategic location on the Mediterranean coast and its Greco-Egyptian culture made it a hub for commerce and exchange, attracting a diverse population including Jewish settlers from Palestine.