Smeatons Eddystone Lighthouse was built of Portland
stone. To secure the structure to the underlying rock, the lower courses
were dovetailed, and set into corresponding dovetails that had been cut
into the rock. For higher courses, the stones were carefully interlocked
and pinned to the levels above and below. The resulting structure was
extremely secure, and it withstood the battering of the sea for one
hundred and thirty years. In the end, it was the rock below that began to
fail, and not the lighthouse above it, and Smeatons tower was replaced
in 1882 by a taller lighthouse on a nearby rock.
The illustration is from the second edition of Smeatons
account of the building of the lighthouse, published two years after the
first in 1793. It shows the plans for the six lower courses of the
lighthouse, which when completed provided a level foundation for the rest
of the tower.