Roberts Island complex facts for kids

The Roberts Island complex is an ancient archaeological site in Citrus County, Florida, located near the Gulf of Mexico. It dates back to the late Woodland period, a time when early Native American cultures thrived. This special place is found on an island in the Crystal River, right between the river's start and where it flows into the Gulf. It's actually a separate part of the larger Crystal River Archaeological State Park. The site includes three large shell mounds and three middens (ancient trash heaps made of shells and other things). Two of these mounds might have even had sides that looked like steps! The Roberts Island complex became important as the nearby Crystal River site started to decline, around the 7th or 8th century.

What is Roberts Island?

Roberts Island sits where the Crystal River splits into two, with the Salt River branching off. Both of these rivers are affected by the tides. The Roberts Island site is about half a kilometer (0.3 miles) downstream from the main Crystal River archaeological site. The soil on Roberts Island is mostly a type called Hallandale-Rock Outcrop, but some areas have soil created by the ancient people who lived there.

The island's main natural area is a Prairie hammock, which is a type of forest. It's surrounded by tidal marshes and the ancient shell mounds. These shell mounds are now covered by thick forests. Scientists believe these mounds were mostly built on limestone outcrops in these hammocks or prairies, though some might have been in the tidal marshes. Most of Roberts Island remains untouched, but a couple of houses are still privately owned. The entire Crystal River site has a special archaeological code, 8CI1, but different parts of Roberts Island have their own codes, like 8CI36, 8CI37, 8CI39, 8CI40, 8CI41, and 8CI576. Roberts Island became part of the state park in 1996.

While the main Crystal River Site has been studied for over 100 years, the mounds on Roberts Island didn't get much attention from archaeologists until the 1950s. That's when Ripley and Adelaide Bullen first reported on some of the features. Later, in 1993, Gary Ellis described another important feature. Experts from the Florida Department of Environmental Protection believe the ancient treasures and history at Roberts Island are just as important as those at the main Crystal River site.

Mound A: The Largest Mound

The biggest site on Roberts Island is called 8CI41. It's an island in a marsh, about 200 meters (656 feet) long and 20 to 50 meters (65 to 164 feet) wide. This island is almost completely covered by a midden, and Mound A was built right on top of it.

People likely started living on this small island when the sea level was about 1 meter (3 feet) lower than it is today. Radiocarbon dating shows that people first lived here between the years 571 and 747. A thick layer of shell midden, about 1 to 1.5 meters (3 to 5 feet) deep, was built up on the island until about 779 to 982. Mound A was then built from oyster shells on top of this midden, probably around the same time the last layer of the midden was added.

This mound has a flat top. It's 32 meters (105 feet) long and 29 meters (95 feet) wide at its base. The top is 21 meters (69 feet) long and 14 meters (46 feet) wide, and the mound stands 4 meters (13 feet) high. It runs north to south. There might have been a ramp on the east side, leading down from the top to a possible open area (plaza) about 40 meters (131 feet) long.

Mound A is covered by a layer of dark brown sandy soil with small bits of crushed shell. Below that is a layer of dark grey sandy soil, also with some crushed shell. The main part of the mound is made of whole oyster shells. Scientists have found signs that the mound had stepped sides, like stairs. They used a special radar (ground-penetrating radar) and dug a trench to see these steps. These steps are unique and haven't been found on other mounds in this part of Florida. It seems there were about six steps above the ground, each about 55 centimeters (22 inches) high.

The mound was built almost entirely from oyster shells. Evidence suggests it was built quite quickly, possibly in less than a year, as all the shells seem to have been collected in the late fall and winter. While the very top wasn't dug up, no signs of a building were found there.

Mound B: A Smaller Temple Mound

Site 8CI40, also known as Crystal River 6, is a small island northeast of Mound A. It's almost completely covered by a rectangular mound called Mound B. This mound is smaller and lower than Mound A. It's 56 meters (184 feet) long and 30 meters (98 feet) wide at its base. The flat top is 40 meters (131 feet) long and 18 meters (59 feet) wide.

Early archaeologists described 8CI40 as a "temple mound" because of its steep sides and flat top. Mound B was also built from oyster shells and is about the same age as Mound A. A house built in the 1950s now sits on top of this mound. Like Mound A, Mound B has thin surface layers of soil. The top layer contains many items from the 20th-century house. The layer below is dark grey sandy soil with crushed shell. The core of Mound B, like Mound A, is made of whole oyster shells.

Scientists have also found evidence of steps on the sides of Mound B, though they are not as clear as those on Mound A. Each step seems to be about 1 meter (3 feet) wide and 20 centimeters (8 inches) high. Based on radiocarbon dates and pottery found, Mound B was built around the same time as Mound A, likely in the 11th century AD.

Mound C: Completing the Complex

Site 8CI36 is another small island, located southeast of Mound A. It has a rectangular mound called Mound C, which is about 1 meter (3 feet) high. Mound C is 33 meters (108 feet) long and 26 meters (85 feet) wide at its base. Its top is 25 meters (82 feet) long and 17 meters (56 feet) wide. This mound was also built using oyster shells. The exact time when Mound C was built isn't known for sure.

The three mounds form an interesting pattern. The distance from the center of Mound A to Mound B is 93 meters (305 feet). From Mound A to Mound C is 103 meters (338 feet), and from Mound B to Mound C is 145 meters (476 feet). This arrangement, forming an approximate triangle, along with their similar ages, suggests that the three mounds were planned and built together as one "integrated architectural complex." They surround an area that might have been a plaza on the east side of Mound A.

Ancient Shell Middens

Besides the mounds, there are also important shell middens at Roberts Island:

• 8CI36 (Crystal River 2) is a shell midden about 23 meters (75 feet) across.
• 8CI37 (Crystal River 3) is a larger shell midden, about 46 meters (150 feet) across. Pottery from the Weeden Island culture and Safety Harbor culture has been found here.
• 8CI39 (Crystal River 5) is described as a narrow ridge made of shells. Pottery from the Deptford culture, Weeden Island, and Safety Harbor cultures has been discovered at this site.

Taking Over from Crystal River

The main ceremonial center at the Crystal River site began very early, probably between the years 69 and 225. It grew into a very important place, known as the southernmost major ceremonial site linked to the Hopewell tradition. However, its importance started to fade by the 7th or 8th century, and it was no longer used as a ceremonial center by the 10th century, though some people still lived there.

The pottery styles found at Roberts Island are very similar to those at the Crystal River site. This suggests that people and their important ceremonies gradually moved from the Crystal River site to Roberts Island. However, there was a big change in what people ate during feasts. At Roberts Island, feasts mainly featured oysters and other shellfish. At Crystal River, almost half the food at feasts came from mammals, but this type of meat almost disappeared from feasts at Roberts Island.