The Dumbuck structure, when occupied, adjoined and commanded a _ford_
across the undeepened Clyde of uncommercial times. So Sir Arthur
Mitchell informs us. {51a} The Langbank structure, as I understand, is
opposite to that of Dumbuck on the southern side of the river. If two
strongly built structures large enough for occupation exist on opposite
sides of a ford, their purpose is evident: they guard the ford, like the
two stone camps on each side of the narrows of the Avon at Clifton.
Dr. Munro, on the other hand, says, "the smallness of the habitable area
on both "sites" puts them out of the category of military forts." {51b}
My suggestion is that the structure was so far "military" as is implied
in its being occupied, with Langbank on the opposite bank of Clyde by
keepers of the ford. In 1901 Dr. Munro wrote, "even the keepers of the
watch-tower at the ford of Dumbuck had their quern, and ground their own
corn." {52a} This idea has therefore passed through Dr. Munro's mind,
though I did not know the fact till after I had come to the same
hypothesis. The habitable area was therefore, adequate to the wants of
these festive people. I conjecture that these "keepers of the
watch-tower at the ford" were military "watchers of the ford," for that
seems to me less improbable than that "a round tower with very thick
walls, {52b} like the brochs and other forts of North Britain," was built
in the interests of the navigation of Clyde at a very remote period.
{52c}
But really all this is of no importance to the argument. People lived in
these sites, perhaps as early as 400 A.D. or earlier. Such places of
safety were sadly needed during the intermittent and turbulent Roman
occupation.