Premise: It is housed in a Martello A series of such towers, some 12 m (40 ft) high and 2.5 m (8 ft) thick, were constructed along the coast at the beginning of the 19th century to guard against invasion by Napoleon.

Hypothesis: A number of these towers, which were built to guard against invasion by Napoleon, were built along the coast in the 19th century.
Relation: entailment