ion does not seem to have been complete or permanent, for during
the latter empire, there were certainly sovereigns of this part of Arabia,
in some degree independent, whose influence and alliance were courted by
the Romans and Persians, whenever a war was about to commence between these
two powers.

From this sketch of the trade of the Arabians from the earliest period, we
may conclude, in the first place, that when navigation was in its infancy,
it was confined, or almost entirely so, to a land trade carried on by
caravans; and that Petra was the centre to which these caravans tended from
the east and the south, bringing with them from the former the commodities
of India, and from the latter the commodities of the more fertile part of
Arabia. From Petra, all these goods were again transported by land to the
shores of the Mediterranean and to Egypt. In the second place, when
navigation became more commonly known and practised, (and there is good
reason to believe that it was known and practised among the Arabians,
especially those near the Persian Gulf, at a very early period,) a portion
of the Indian commodities, which before had been carried by land to Petra
were brought by sea to Sabaea. It appears that in the age of Agatharcides,
the monopoly of the trade between India and Europe by this route was wholly
possessed by the Sabeans; that, in order to evade the effects of this
monopoly, the Greeks of Egypt found their way to Aden and Hadraumaut, in
Arabia, and to Mosullon on the coast of Africa. Here they met with other
Arabians, who at this time also traded to India, and sold them Indian goods
at a cheaper rate. And, lastly, we have seen that these ports on the
southern coast of Arabia, and on the coast of Africa, were frequented by
the merchants of Egypt, till, by the discovery of the monsoon, their ships
were enabled to sail directly to India. It is undoubtedly true that before
this discovery, single ships occasionally reached India by adhering to the
coast all the way, but the direct communication was very rare. After the
nature of the monsoon was thoroughly understood, and it was ascertained
that complete dependence could be placed on its steadiness and regularity,
and that by its change, the ships could be brought as safely and quickly
back from India, as they had reached it, the ancients, who at first only
ventured to the mouth of the Indus, gradually made their way down the
western coast of the Indian peninsula.