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It seems a typical scene of urban decay: abandoned buildings, crumbling walls, trash and broken wine bottles.

Yet it's more than 1,500 years old. Engineers uncovered these ruins of an ancient Byzantine port during drilling for a huge underground rail tunnel.

Like Romans, Athenians and residents of other great historic cities, the people of Istanbul can hardly put a shovel in the ground without digging up something important.

But the ancient port uncovered last November in the Yenikapi neighborhood is of a different scale: It has grown into the largest archaeological dig in Istanbul's history, and the port's extent is only now being revealed.

Archaeologists call it the "Port of Theodosius," after the emperor of Rome and Byzantium who died in A.D. 395. They expect to gain insights into ancient commercial life in the city, once called Constantinople, that was the capital of the eastern Roman, Byzantine and Ottoman empires.

Dr. Cemal Pulak, of Texas A&M University and the Institute of Nautical Archaeology in Turkey, said the engineers working on the tunnel project were surprised to stumble on the ruins. But he said archaeologists knew from ancient documents the port was somewhere around Yenikapi.

"This was the ancient harbor of Byzantium, the Theodosian harbor," Pulak said, pointing to the dusty site around him, which he said was probably an expansion of an earlier port known as Eleutherion.

So far, the 17 archaeologists, three architects and some 350 workers at the site have found what they think might be a church, a gated entrance to the city and eight sunken ships, which have Pulak particularly excited.

He believes the ships were wiped out all at once in a giant storm.

He said the wooden boats, all apparently destroyed around 1000, make up a sort of "missing link" in the history of shipbuilding because of the fusion of old and new techniques in a single boat.

"When I came here and saw those ships, the lower part built by the ancient method, the upper part by the modern method, it was more or less the missing link," Pulak said.

The site is huge, about four city blocks long by two to three wide. Hundreds of workers dig with picks and shovels, dusting items off or rolling wheelbarrows up wooden planks.

Walking around, workers kick up pieces of ancient pottery and bones. Most of the items are ancient trash: broken pottery that sailors tossed from a ship or animal bones from a nearby slaughterhouse that were thrown into the harbor.

Digging for the Marmaray tunnel has also led to archaeological finds in the Uskudar district on the Asian side of Istanbul and Sirkeci and Veznedar on the European side. Giant machines constructing the tunnel are dredging up artifacts from the sea floor in the Bosporus.

Most of the tens of thousands of pieces likely to be uncovered will be cataloged and then reburied where they were found, said Metin Gokay, a scientist at the Istanbul Archaeological Museum. Only a small percentage will qualify as museum-quality pieces, while others will be used for research.

Modern-day Turkish coins will be left with the reburied items as markers to show the area has been disturbed, just in case archaeologists many centuries later dig the site up again, Gokay said.

Part of the value of the site is its abundance of ancient trash. Refuse is one of the best ways to study how people lived.

Hundreds of cracked clay pots already have indicated how merchants carried wine, olive oil and other trading items, and some carry markings that give clues about how the pots were handled and traded.

"We've found things that shed important light on the history of Istanbul," said Ismail Karamut, head of the archaeological project.

Officials said they plan to build a museum on part of the site and incorporate it into the rail project, which is meant to ease traffic on the jammed streets in the city of 15 million people.

The excavation site is where the Marmaray tunnel was supposed to link up with a subway station in a massive underground station. Planners now say they are considering moving the underground link to a spot farther outside Istanbul.

All around, the ancient is hemmed in by the new. One partly revealed structure is thought to be a church, but the archaeologists would have to dig up the other half to be sure — and it's under an apartment building.