Merchants with goods from Rome would leave Egypt by boat sometime around the month of July so as to travel with favorable wind conditions. The summer monsoon winds blow from the southeast and the monsoon winds during the winter would blow northwest. Early sailors took advantage of their knowledge of the wind changes and learned to plan their trading schedules around these weather changes. Merchants during the summer months would sail down the Red Sea to the gulf of Aden (Southern tip of the Arabian Penninsula and Somalia), from there they either unload their goods and trade with the locals or would sail with the summer winds across the Indian Oceans to India. The Red Sea was a dangerous sea route, for there are many reefs that a ship could strike and at various time periods pirates were a serious threat. The summer monsoon winds were the most treacherous time to travel on the Indian Ocean for ancient and even modern day sailors. The winds are incredibly strong and storms are very violent and frequent during the summer monsoons. Yet despite these hazards sailors risked their lives and traveled this dangerous route frequently, a successful voyage meant great wealth to the sailors that survived the ordeal.
Around November the winds would shift to blow to the northwest. The voyage from Egypt to India could take around 3-4 months if there are favorable wind conditions. There was enough of a gap between the shifts in the wind to allow the ancient traders to unload their goods and load their ships with items of trade. Since the summer monsoon winds were so strong, early sailors had to develop ships that could withstand the sea. The Greco-Roman sailors knew that only ships with a very strong hull and ships that could transport a large load would survive the rigorous journey across the Indian Ocean. They developed a unique shipbuilding concept in order to meet these demands.
Instead of laying out the keel, the stern and stem post first, then attaching the frames to the hull, and finally adding the planks, they did this in reverse. They put the planks together first and then added the frames, stern and stem post, and then the keel. The Greco-Roman sailors were able to build stronger ships through this process. The ships were stronger because the planks were held to one another by doles and mortise, not by the keel and the stern and stem posts. Only ships that could carry a large load of goods were worth investing money in to the ancient merchants. Ships that traveled the Indian Ocean were nearly 180 feet long and could carry a cargo of close to a thousand tons.
The Romans traded gold and silver, various types of food, and cloth with the Arabs and Indus valley for silk, pearls, spices, slaves, incense, and ivory. There were over land routes that connected Rome with India, but the Roman traders preferred to take sea routes to India for a variety of reasons. At various times in history these overland routes fell under the control of various kingdoms that were or were not friendly with the Roman Empire. These rulers would sometimes exact heavy taxes on traders who used these overland routes and did much to or little to protect the traders. Also these overland trade routes were sometimes not very well maintained, which made travel very difficult and then there was the problem of raiders attacking traders. To bring large amount of goods overland required a large number of pack animals who could only carry so much, travel so far and fast, and required great attention to their physical needs. Even though traveling overseas could be treacherous, traders could carry more goods at a faster pace than they could by traveling overland.