204 Reason and Its Rivals (ca. 1550– 1815)to the demands of an eternal and universal natural law on high. It has been
observed that, in the Middle Ages, it was not uncommon for states to make
claims of sovereignty over areas of the seas. Natural- law writers consis-
tently rejected such claims, though, asserting that the sea was common to
all for the two key operations of fi shing and navigation.
It was conceded, however, even by champions of freedom of the seas, such
as Grotius, that at least some kind of property right could be acquired, by
way of occupation, over certain very small areas of the sea, such as inlets
largely enclosed by land. Th e question was the kind of right. Some writers
contended that occupation could confer full own ership, or dominium in the
parlance of Roman law. Th is was on the model of the Roman law of occupa-
tion, which (as observed earlier) was one of the “natural” modes of acquir-
ing title to property. Others contended, though, that the more apposite
concept was the Roman-law principle of imperium, according to which the
rights of the coastal state were strictly contingent upon the actual exercise of
control. So long as the control was actually and eff ectively exercised, a legal
right of possession would be recognized by other parties. But if that control
lapsed, then the area reverted to its prior status of being free to all.
Th is imperium argument was put by another of the opponents of James I’s
fi sheries claim, French lawyer and diplomat Pierre Jeannin. A coastal state,
he maintained, can only assert its power over maritime areas which are
within range of its artillery fi re. Beyond that point, the sea must be free to
all. Th is appears to be the fi rst appearance in print of what became known,
for obvious reasons, as the “cannon- shot rule,” but it also seems that Jean-
nin was expressing a position widely held at the time. In all events, the
cannon- shot principle came to be widely accepted in the course of the eigh-
teenth century, largely on the strength of Bynkerhshoek’s advocacy of it in
his pamphlet of 1703 on maritime law.
In the course of the eigh teenth century, the nature of the coastal state’s
right underwent a subtle, but signifi cant, alteration: from a basis of impe-
rium to one of dominium. Th e idea of imperium implied that a coastal state
could have legal title to any area of the sea which it actually policed— that is,
to areas where artillery was physically deployed. Th is position was not ad-
hered to, however. It came to be agreed that what coastal states possessed was
true dominium over their off shore areas, with the cannon- shot principle now
functioning merely as a unit of account for mea sure ment. Th ere continued to