Archaeologist Ferudun Ozgumus stands in what is believed to be a Byzantine-era substructure in Istanbul.
The winding streets of old Istanbul are an overlapping cacophony of seagulls, ship horns and vendors of colorful fresh fruit. Shady fig trees cluster near crumbling Byzantine walls and sweeping Ottoman palaces, remnants of the empires that conquered and lost this strategic point on the Bosporus Strait, which formed the seat of the Eastern Roman Empire.
Underneath it all is an ancient world that's almost invisible, unless you know where to look.
"Can you imagine my excitement when I saw this for the first time?" exclaims archaeologist Ferudun Ozgumus, as he leads the way down a rickety wooden staircase into a cavernous structure deep beneath a carpet shop. "It was full of debris as far as that corner of the arch," he says, pointing across the space to a point 15 feet overhead. "We were crawling!"