Britain seem to have been exported by foreign ships, and the commodities
given in exchange brought by these.

In our account of the commerce of the Phoenicians, their trade to Britain
for tin has been described. Pliny, in his chapter on inventions and
discoveries, states that this metal was first brought from the Cassiterides
by Midacritus, but at what period, or of what nation he was, he does not
inform us. This trade was so lucrative, that a participation in it was
eagerly sought by all the commercial nations of the Mediterranean, and even
by the Romans, who, as we have seen, were not at this period, much given to
commerce. This is evident, by the well known fact, of one of their vessels
endeavouring to follow the course of a Phoenician or Carthaginian vessel,
in her voyage to Britain. The Greeks of Marseilles, according to Polybius,
first followed, successfully, the course of the Phoenicians, and, about 200
years before Christ, began to share with them in the tin trade. Whether, at
this period, they procured it exclusively by direct trade with Britain, is
not known; but afterwards, as we have already mentioned, Marseilles became
one of the principal depots for this metal, which was conveyed to it
through Gaul, and exported thence by sea.

If we may believe Strabo, the Romans had visited Britain before it was
invaded by Caesar, as he expressly mentions that Publius Crassus made a
voyage thither: if he means P. Crassus the younger, he was one of Caesar's
lieutenants in Gaul; and, as he was stationed in the district of the Vanni,
it is not improbable that he passed from thence into Britain; or he may
have been sent by Caesar, at the same time that Volusenus was sent, and for
the same purpose.

However this may be, there was no regular intercourse between Britain and
Rome till some time after Caesar's invasion; in the time of Tiberius,