A naumachia was the reenactment of a naval battle in a basin or on a lake, a popular albeit costly – and for the participants deadly – entertainment of the masses in ancient Rome. The term naumachia was also used for the location at which the games took place.
Our current read, Sand of the Arena, opens with an imaginative happening of the naumachia of Nero – “…he also exhibited a naval battle in salt water with sea monsters swimming about in it” according to Suetonius’ Life of Nero.
. In Nero's naumachia there were sea-monsters swimming about in the artificial lake (Suet. Nero, 12; Dion Cass. LXI.9), and Claudius had a silver Triton placed in the middle of the lake Fucinus, who was made by machinery to give the signal for attack with a trumpet (Suet. Claud. 21) . Troops of Nereids were also represented swimming about (Martial, de Spect. 26). I n the sea-fight exhibited by Titus there were 3000 men engaged (Dion Cass. LXVI.25), and in that exhibited by Domitian the ships were almost equal in number to two real fleets (paene justae classes, Suet. Dom. 4). In the battle on the lake Fucinus there were 19,000 combatants (Tacit. Ann. XII.56) and fifty ships on each side (Dion Cass. LX.33).
http://romanhistorybooks.typepad.com/roman_history_books_and_m/2007/03/naumachia.html#tp===========================================================================================
For the amount of money harper has blown, you would think we could get a sea monster or two. Maybe if Baird and Duffy went for a swim...