Does the newly discovered Roman quarry mark biblical Gilgal?  The excavator thinks this is possible.  From Haaretz:

Zertal says their working theory is that the site is Galgala, biblical Gilgal, mentioned on the sixth-century Madaba mosaic map. The cave, buried 10 meters underground, is about 100 meters long, 40 meters wide and 4 meters high, is the largest artificial cave so far discovered in Israel.
Potsherds found in the cave and the carvings on the columns led Zertal to date the first quarrying of the cave to around the beginning of the Common Era. It was used mainly as a quarry for 400 to 500 years,” but other finds give the impression it was used for other purposes, perhaps a monastery or even a hiding place,” Zertal said.
Zertal said scholars wondered why people would dig a quarry underground considering the effort needed to just to pull the stones out of the ground.
A possible answer may be in the famous Madaba Map of ancient Palestine, found in Jordan. In it, a place named Galgala is marked and an accompanying Greek word meaning “12 stones.” The map also depicts a church near the site. Archaeologists say they have found two ancient churches near the cave.
According to Zertal, scholars had always assumed that “12 stones” refered to the biblical story of the 12 stones the Israelites set up at Gilgal after they crossed the Jordan.
However, the discovery of the quarried cave may mean the reference was to a quarry established where the Byzantines identified Gilgal. Zertal explains that in antiquity sanctuaries were built out of stones from sacred places.

The rest of the article is here. 

I would note that there is sometimes a big difference between a biblical site and what Byzantines thought was a biblical site.  In any case, the quarry’s location, 3 miles north of Jericho, is approximately where biblical scholars have supposed ancient Gilgal may have been located.  What has always been lacking is any archaeological evidence for a site from the time of Joshua.  A Roman quarry does not provide that evidence, but it may be a step in the right direction.

References to Gilgal in the Bible include Josh 4:19-20, Josh 10:6-7, 1 Sam 11:14-15, 1 Sam 13:4-15, 2 Sam 19:15; 2 Kings 2:1, Hos 4:15, and Amos 4:4.

HT: Joe Lauer

UPDATE (6/22): Thanks to Joe Lauer for sending along links to articles with photos.  The University of Haifa has issued a press release which includes four high-resolution photos.  Ynet includes a slideshow with six images, including one of the cave’s entrance.

UPDATE (6/25): National Geographic has an article about the discovery, including some quotations from Jodi Magness.

Jericho and Gilgal on the Medeba Map
Outlined in red is “Gilgal, also the Twelve Stones”
Below and to the right is the city of “Jericho,” surrounded by palm trees
The Jordan River is at the top, with the fish on the right swimming away from the Dead Sea

For more about the Medeba Map, see this BiblePlaces page.

The largest manmade cave in Israel was found 3 miles north of Jericho, and may have been used as a monastery in later years.  From the Jerusalem Post:

An artificial underground cave, the largest of its kind in Israel, was discovered in the Jordan Valley during excavations by the Haifa University’s Department of Archaeology. Prof. Adam Zertal, who headed the dig, assessed that the cave was used as a quarry in the Roman era. Various carvings were found on the cave’s walls, including some of crosses, leading to the notion that the cave might have also hosted an ancient monastery. The cave, sprawling over four dunams [1 acre] ten meters [32 feet] under the face of earth, is located some four kilometers [2.5 miles] north of Jericho. It was discovered at the end of March 2009 as part of a Haifa University dig which began in 1978, and is the largest man-made cave ever uncovered in Israel. The cave’s main hall is supported by 22 pillars, on which are engraved 31 crosses, a zodiac-like symbol, roman numerals and a Roman legion’s pennant. Judging by the findings, Prof. Zertal dated the cavern to around 1 CE. "Initially, the place was utilized as a quarry, which was active for 400-500 years. But the other findings definitely give the impression that the cave was used for other purposes, such as a monastery, and perhaps even a hideaway," said Zertal.

The story is also covered by Haaretz and Reuters.