Strabo Geography 5.4.6

[6] The Lucrine gulf extends in breadth as far as Baïae; it is separated from the sea by a bank eight stadia in length, and the breadth of a carriage-way; this they say was constructed by Hercules when he drove away the oxen of Geryon. But as the wave covered its surface in stormy weather, rendering it difficult to pass on foot, Agrippa has repaired it. Small vessels can put into it, but it is useless as a harbour. ¹ It contains abundant oyster-beds. Some take this to be the Acherusian Lake, while Artemidorus confounds it with Avernus. They say that Baïae took its name from Baius one of the companions of Ulysses, and Misenum from Misenus. Beyond is the strand and city of Dicaearchia. Formerly it was nothing but a naval station of the Cumaei. It was built on an eminence. But at the time of the war with Hannibal, the Romans established a colony there, and changed its name into Puteoli, ² [an appellation derived] from its wells; or, according to others, from the stench of its waters, the whole district from hence to Baïae and Cumae being full of sulphur, fire, and hot-springs. Some too are of opinion that it was on this account [that the country about] Cumae was named Phlegra, and that the fables of the giants struck down by thunderbolts owe their origin to these eruptions of fire and water. This city has become a place of extensive commerce, having artificially constructed harbours, which were much facilitated by the facile nature of the sand, which contains much gypsum, and will cement and consolidate thoroughly. For mixing this sand with chalk-stones they construct moles in the sea, thus forming bays along the open coast, in which the largest transport ships may safely ride. Immediately above the city lies the Forum-Vulcani, ³ a plain surrounded with hills which seem to be on fire, having in many parts mouths emitting smoke, frequently accompanied by a terrible rumbling noise; the plain itself is full of drifted sulphur.