*grumbles about stupid server which swallowed his first reply*

Anyway mate Deceres are ships which only the House of Scipii can build, the House of Scipii gets the strongest navy in the game

An Awesome Temple of Neptune allows them to build a Corvus Quinqereme which is a slightly stronger quinqereme vessel.

A Pantheon of Neptune allows them to build a Decere, which takes three turns to construct and is desribed in the unit description as 'a Dreadnought of the ancient world'.

The temples also allow Scipii Admirals in port to pick up 'Priest of Neptune' ancillaries which aid their command rating.