A battle royale over an estimated $500 million treasure that a Florida deep-sea salvage company found last year is due for a fresh round in court in Florida on Monday.

The Spanish government now says the 500,000 silver and gold coins that the company, Odyssey Marine Exploration, found last year in the Atlantic Ocean near Spain came from one of its ships that sunk in a 19th-century naval battle. Spain wants the entire treasure returned, but Odyssey insists Spain may have no right to it.

Lawyers for both sides are due to present arguments Monday morning in a U.S. federal court in Tampa, Florida, in another round of the case that started last year, Odyssey spokeswoman Natja Igney told CNN.

Odyssey found the coins last year and quietly airlifted them in crates from Gibraltar, a British colony on Spain’s southern tip, to Florida for safekeeping. The company then said it was unclear how the huge quantity of coins it found on the seabed had gotten there. It declined to reveal the location, citing security reasons, and mysteriously dubbed the site “Black Swan.”

But the Spanish government, at a recent Madrid news conference, said it’s really not so complicated.

“The mystery is over,” said James Goold, a U.S. lawyer representing Spain, told the news conference. “Using a variety of methods to conceal what it was doing, Odyssey Marine Exploration stripped the gravesite that is the Spanish navy warship Nuestra Senora de las Mercedes of coins and other objects. The coins and other artifacts that Odyssey took from the site are documented to have been on the Mercedes,” Goold said.

The Mercedes was a 34-gun frigate, a ship very common at the time in the Spanish navy. The Mercedes left Peru, stopped in Uruguay and was just a day’s sail from Spain when the four-ship Spanish squadron was attacked by a British fleet in October 1804, according to a Spanish government’s filing to the Florida court. (more…)