COLLINSVILLE — The ancient Mississippians apparently used a ritual drink that was highly caffeinated, but you wouldn't want it to replace your morning coffee.

Archaeologists digging at the Cahokia Mounds site near Collinsville have found evidence that the prehistoric Native Americans who lived throughout the metro-east in the ancient city of Cahokia adopted a ceremonial ritual involving what was called the Black Drink.

The ritual probably did not originate here, according to assistant site manager Bill Iseminger. But apparently the Mississippians adopted it, because biomarkers in a ceremonial cup were found last year and the University of Illinois team confirmed it is a residue from a type of holly that only grows around the Gulf Coast.

"It was part of the spiritual and physical cleansing," Iseminger said.

The Black Drink had six times the amount of caffeine as coffee, which would give a boost to warriors going into battle.

However, it also causes vomiting, which they may have seen as purifying, Iseminger said.

It is further evidence that Cahokia traded with cultures far away, he said. Researchers already had evidence that long-distance trade existed; they have found seashells and shark's teeth in previous digs, items unlikely to occur naturally in the metro-east.

Iseminger said this particular holly, known as Yaupon holly or ilex vomitoria, has never grown here -- more evidence for trade.

"It's not the Christmas holly we're used to, and only grows in the very southern part of the U.S.," he said.

The cups -- which they call "beakers" -- are dated after 1200 AD. The leaves are roasted, then boiled to extract the caffeine, as was recorded centuries later in the American southeast by other tribes.

The ritual is known from some paintings dated to 1500 AD that show other cultures drinking the Black Drink out of shell cups or conch shells, Iseminger said.

It's not entirely clear who adopted the ritual first, he said, but since the berries originated in the south, it's likely that it began there and was adopted by Cahokia as a new religion in its later years. However, the findings recently published in an academic journal said this dates the ritual of the Black Drink centuries earlier than previously suspected.

The Mississippian culture vanished centuries before European settlers came to this region, leaving only the mounds scattered throughout the area as evidence of a civilization that held 50,000 residents at its peak -- larger than London at the time.

Other discoveries this year included a giant platformlike rectangular anomaly buried along the old creek bank, which Iseminger said they are calling Feature X -- at least until they figure out what it is.

"We're not clear yet if it was an old mound that was reburied, if they were adding soil to the creek bank, or it might have been a platform for a mound or some other kind of construction," Iseminger said.

The anomaly showed up on a magnetic resonance scan of soil disturbance, Iseminger said. It disclosed a large, rectangular feature beneath the ground. Feature X is about 150 feet long.

The old creek lay where Interstate 55-70 lies today, and they may have been adding soil to extend the creek bank, Iseminger said.

"It will take us some more work to find out," he said.

Contact reporter Elizabeth Donald at edonald@bnd.com or 239-2501.