One way to understand the implications of the archaeological discoveries at Pattanam is to delve into the amazing wealth of data from the excavations at the lost Ptolemic-Roman port city of Berenike, on Egypt’s Red Sea coast. During the Ptolemic-Roman period (third century B.C. to sixth century A.D), Berenike served as a key transit port between ancient Egypt and Rome on one side and the Red Sea-Indian Ocean regions, including South Arabia, East Africa, India and Sri Lanka, on the other.
This ancient port city was well-connected by roads from the Nile that passed through the Eastern Desert of Egypt and also by sea routes from the Indian Ocean regions. Cargoes unloaded at Berenike and other Egyptian Red Sea ports (such as Myos Hormos, now lost) used to be taken along the desert roads to the Nile and from there through the river to the Mediterranean Sea and across, to the Roman trade centres.
Exotic goods from Rome and Egypt flowed into Berenike along the same desert road before being loaded into large ships bound for the Indian Ocean.
By the end of the second century B.C., the Egyptians and the Romans finally learnt the skill of sailing with the monsoon winds across the Indian Ocean (“from the Arabs and other Easterners”). Voyages from Berenike for the riches of the Malabar coast therefore became “faster, cheaper, but not less dangerous”.
According to most accounts, one of the major centres in India that ships from Berenike travelled to, along with the monsoon winds, was the emporium of Muziris, on the Malabar coast.
For anyone interested in investigating more about these trade connections via the Egyptian port of Berenike I would recommend the book Indo-Roman Trade: From Pots to Pepper by Roberta Tomber. Here's the write-up from the back of the book:
This book brings together for the first time archaeological findings from key ports throughout the Indian Ocean - the Red Sea, South Arabia, the Gulf and India - to build up a balanced picture of relations between East and West. Combined evidence from artefacts and documents reveals a complex situation whereby ordinary goods were carried alongside the more costly items - such as pepper, aromatics and gems - that drove the trade. Here the focus is on ordinary artefacts that uncover a network of Romans, Arabs, Sasanians and Indians who participated in the trade. The evidence from ceramics, especially, shows the interplay between these different ethnic groups, where they lived, when the trade was active, and even how it was organised.The account is arranged geographically, drawing on new evidence from the author's experience of archaeological sites and materials on the Red Sea and in India. A final chapter sketches the changing fortunes of trade between the first century BC and the seventh century AD in the light of these important new archaeological discoveries.