To the northwest of Lothal (2400 BCE) lies the Kutch peninsula. Proximity to the Gulf of Khambhat allowed direct access to sea routes. Lothal's topography and geology reflects its maritime past.
The region around the Indus river began to show visible increase in both the length and the frequency of maritime voyages by 3000 BCE. Optimum conditions for viable long-distance voyages existed in this region by 2900 BCE. Mesopotamian inscriptions indicate that Indian traders from the Indus valley—carrying copper, hardwoods, ivory, pearls, carnelian, and gold—were active in Mesopotamia during the reign of Sargon of Akkad (c. 2300 BCE).
Gosch & Stearns write on the Indus Valley's pre-modern maritime travel:Evidence exists that Harappans were bulk-shipping timber and special woods to Sumer on ships and luxury items such as lapis lazuli. The trade in lapis lazuli was carried out from northern Afghanistan over eastern Iran to Sumer but during the Mature Harappan period an Indus colony was established at Shortugai in Central Asia near the Badakshan mines and the lapis stones were brought overland to Lothal in Gujarat and shipped to Oman, Bahrain and Mesopotamia.
Archaeological research at sites in Mesopotamia, Bahrain, and Oman has led to the recovery of artefacts traceable to the Indus Valley civilisation, confirming the information on the inscriptions. Among the most important of these objects are stamp seals carved in soapstone, stone weights, and colourful carnelian beads....Most of the trade between Mesopotamia and the Indus Valley was indirect. Shippers from both regions converged in Persian Gulf ports, especially on the island of Bahrain (known as Dilmun to the Sumerians).
Numerous small Indus-style artefacts have been recovered at locations on Bahrain and further down the coast of the Arabian Peninsula in Oman. Stamp seals produced in Bahrain have been found at sites in Mesopotamia and the Indus Valley, strengthening the likelihood that the island may have acted as a redistribution point for goods coming from Mesopotamia and the Indus area....There are hints from the digs at Ur, a major Sumerian city-state on the Euphrates, that some Indus Valley merchants and artisans (bead makers) may have established communities in Mesopotamia.
The world's first dock at Lothal (2400 BCE) was located away from the main current to avoid deposition of silt. Modern oceanographers have observed that the Harappans must have possessed great knowledge relating to tides in order to build such a dock on the ever-shifting course of the Sabarmati, as well as exemplary hydrography and maritime engineeri. This was the earliest known dock found in the world, equipped to berth and service ships. It is speculated that Lothal engineers studied tidal movements, and their effects on brick-built structures, since the walls are of kiln-burnt bricks. This knowledge also enabled them to select Lothal's location in the first place, as the Gulf of Khambhat has the highest tidal amplitude and ships can be sluiced through flow tides in the river estuary. The engineers built a trapezoidal structure, with north-south arms of average 21.8 metres (71.5 ft), and east-west arms of 37 metres (121 ft).
Excavations at Golbai Sasan in Odisha have shown a Neolithic culture dating to as early as ca. 2300 BC, followed by a Chalcolithic (copper age) culture and then an Iron Age culture starting around 900 BC. Tools found at this site indicate boat building, perhaps for coastal trade. Fish bones, fishing hooks, barbed spears and harpoons show that fishing was an important part of the economy. Some artefacts of the Chalcolithic period are similar to artefacts found in Vietnam, indicating possible contact with Indochina at a very early period.
In the 3rd millennium BCE inhabitants of the Indus Valley had maritime trading contact with Mesopotamia. As per the Vedic records. the Indian traders and merchants traded with Far East and the Arabia. During the Maurya period (3rd century BC), there was a definite 'naval department' to supervise the ships and trade. The Indian products reached the Romans during the rule of Augustus and Indian merchants earned about 1 million sistreces annually, which was later, not appreciated by the Romans themselves. The Roman historian Strabo mentions an increase in Roman trade with India following the Roman annexation of Egypt.
Coin of Byzantine Theodosius II, found in the excavation of a monastery in Ajanta Caves, India.