New Pompeii

Jurassic Park meets Gladiator in this "irresistibly entertaining" sci-fi adventure set in a world in which technology can transport people from the past to present day (Barnes & Noble Sci-Fi Blog)
 
In the race to control renewable power, an energy giant stumbles on a controversial technology: the ability to transport matter from the deep past. Their biggest secret is New Pompeii, a replica city filled with Romans, pulled through time just before the volcanic eruption.

Nick Houghton doesn't know why he's been chosen to be the company's historical advisor. He's just excited to be there.
 
Until he starts to wonder what happened to his predecessor.
 
Until he realizes that the company has more secrets than even the conspiracy theorists suspect. 

Until he realizes that they have underestimated their captives.