Glasgow's most famous waterway, the River Clyde, is indelibly associated with the city's rise and progress from the 18th century. Yet in earliest times the Clyde was by no means a mighty watercourse. Maps, such as those drawn by Timothy Pont in the late 16th century, reveal that the natural channel was narrow and irregular. A feature of the waterway as it flowed towards the Firth of Clyde was the number of "inches" (or small islands) that marked the landscape. Whiteinch, for instance, was so-called because the area was once wholly detached from the mainland. Moreover, sand and silt from upstream contributed over centuries towards making the Clyde notoriously shallow. Depending on the tides and seasons, the river was only forty centimetres deep at certain stretches.
For all the navigable shortcomings the Clyde Valley had strategic advantages, which encouraged population expansion during the Neolithic period, around 4,000 years BC. It was relatively sheltered, the climate was temperate and the waters provided an abundant source of fish. Over the last 200 years several oaken, dug-out canoes have been excavated in Glasgow, revealing the favoured mode of transport of the early settlers. Some of the vessels indicate that they were even used as ferries. Clyde navigation became more sophisticated when the Romans arrived in Scotland during the 1st century AD. A substantial harbour was constructed, probably at Dumbarton, to receive supplies for the garrisons. Yet despite the Clyde's growing status, it was not the waterway most directly associated with Glasgow's 6th century foundation as an ecclesiastical community. St Kentigern reputedly established the site of his mission beside the Molendinar, a tributary stream of the Clyde, which in later centuries was important as a power-source for city grain mills.
The Clyde became vital for Glasgow's trade after the burgh was erected, under crown authority, during the 12th century. The town's merchants were looking outwards to create trading networks, hoping that the river would provide a direct route to the coastal waters of western Scotland, Ireland and beyond. However, the Clyde's navigable deficiencies meant that sea-going vessels could get no nearer to Glasgow than Dumbarton, necessitating expensive and time-consuming overland journeys to complete the connection. The first stone bridge across the river, built around 1410, visibly demonstrated how technology could be used to enhance the burgh's communications. Thereafter, the problem of access to Glasgow began seriously to be addressed, and tentative efforts to widen and deepen the river were made from at least the mid-16th century.