The eastern portion of Argyll sits between Lochs Lomond and Long.
In the 18th century, a Military Road was built from Dumbarton Castle to Inveraray, following the western side of Loch Lomond until it reached Tarbet, approximately two thirds of the way up the loch. While the original Military Road headed west from Tarbet to Inveraray, a later Military Road continued north alongside the loch to Ardlui at its northern end and on to Crianlarich. This road has since been upgraded and forms the A82, the main route from Dumbarton; parts of the original road still exist.
From Tarbet the A83 heads west to Arrochar, crossing the isthmus that separates Lochs Lomond and Long. The name Tarbet is derived from the Gaelic word Tairbeart, which basically means a narrow stretch of land between water, in this case Loch Lomond and, about a mile to the west, Loch Long. In 1263 Vikings sailed up Loch Long and dragged their boats across this isthmus to Loch Lomond.
As an alternative route, the A814 heads northwest from Dumbarton, following the northern shore of the River Clyde to Helensburgh. From Helensburgh the B832 heads roughly northwest, joining the A82 by Loch Lomond, while the A814 continues north, along the eastern shore of Gare Loch, to Garelochhead. From here the A817 follows Glen Fruin roughly southeast, before then heading northwest to join the A82. Alternatively the B833 heads along the western shore of Gare Loch into the Roseneath peninsula. Meanwhile the A814 continues northwest to the eastern shore of Loch Long and then continues alongside the loch to join the A83 at Arrochar.
From Arrochar the A83 continues round the tip of Loch Long and then climbs through Glen Croe – between Ben Arthur, also known as the Cobbler, and Ben Donich. At the top of the hill is a great viewpoint, looking back down the glen. The route of the old Military Road, referred to as Rest and be Thankful, that was built in the 1740s is still obvious, despite it not being used for some time.
At this point the B828 heads southwest into the Devil's Glen and joins the B839 which heads south to Lochgoilhead or northwest towards Loch Fyne. The A83 continues past Lochan Restil (right) through Glen Kinglas to Loch Fyne where the A815 heads southwest into the Cowal Peninsula. Staying on the A83 and travelling round Loch Fine leads to Inveraray.