Jacki wrote:No idea, but I reckon they used the same company who laid my patio! 
Well, after approx 2000 years, they have had plenty of practice.
I got the inscription translated by a Cambridge classics prof. Although I cannot find the translation at the mo, from memory it contains a "prayer" and details of the builder.
Clue 2.

Same place. No points for Mrs HWV (although, of course she is worth zillions). On a beach nearby we have many times collected semi precious stones (turquoise etc) believed to be coming from a ship sunk in the years BC. After every reasonable tide one or two more of the stones are washed in. The ship was carrying such stones for the various mosaics (pictures of which I haven't put on here in case they are in Google Goggles - brilliant app - library!!).
The whole place is hardly excavated, hardly visited, non-commercial and incredibly impressive. Typically we are the only visitors, typically we wish we had taken a metal detector. It "feels" like it is as it was immediately after its time was up. Amazing.