Archaeological evidence now indicates that Cloggs Cave was used for ritual activities for approximately 25,000 years. Researchers found evidence that people repeatedly carried grasses into the cave, spread them in thin layers and burned them. Sediment later covered the ash, preserving one layer on top of another over thousands of years.

“Here we show that our ancient ancestors picked whole grasses from large landscapes, transported them to Cloggs Cave, spread them in thin layers and burned them. Over time, sediment covered these burnt layers, and over thousands of years each layer was preserved on top of another,” said Dr. El Grono, a postdoctoral fellow at the Australian National University and corresponding author of the study published in Frontiers of Environmental Archaeology.

Microscopic plant remains reveal ancient cave rituals

Grono and researchers from Australia, France and New Zealand examined phytoliths recovered from buried deposits within Cloggs Cave. Phytoliths are microscopic silica structures formed inside plant tissue. They can survive long after the plants themselves have disappeared.

The research followed archaeological excavations conducted in 2019 and 2020. Those excavations aimed to investigate how people collected and used plants in caves in the distant past. The work was commissioned by the Gunaikurnai Land and Water Authority, whose representatives contributed to the research design, fieldwork, interpretation and communication of the results.

“Unlike pollen, which is dispersed by wind or insects, phytoliths mainly accumulate in areas where plants have decayed. In caves, plants cannot grow because of the lack of light, so phytoliths must have been introduced by humans or animals such as possums through their fur or droppings,” Grono explained.

The researchers focused on partly burned phytoliths from an ash layer. These remains could only have been introduced by humans, while unburned phytoliths might have been brought in by either people or animals. Because plants cannot grow naturally in a dark cave, the burned plant remains provide particularly strong evidence that people deliberately carried grass into the site.

Ash layers and a standing stone point to ritual activity

Using microscopes, the researchers classified thousands of phytoliths collected from two excavation pits measuring 1.5 and 2.3 meters deep.

The upper sections of the pits contained 73 thin layers of ash deposited by people approximately 4,400 to 1,600 years ago. Researchers established these ages using photostimulated luminescence and accelerator mass spectrometry carbon dating.

Buried between the layers was a 28-centimeter-high standing stone. Further analysis indicated that ancient people intentionally placed the stone inside the cave for ritual purposes approximately 2,000 years ago.

Ancient people deliberately selected specific grasses

The research team identified 29 types of phytoliths representing grasses, herbs and woody plants. Many were exceptionally well preserved, including delicate silica structures such as hair cells.

Grass phytoliths accounted for 97% of the total sample. They included grasses adapted to temperate or cool conditions, as well as species that generally grow in warm, humid environments.

Phytoliths from grasses in the Chloridoideae family—which tolerate drought and are adapted to warm, dry and arid conditions—were less common. Remains of herbs and woody plants were also rare.

This pattern suggests that ancient cave users did not simply gather every plant growing nearby. Instead, they deliberately selected particular grasses.

Before European settlement, the landscape around Cloggs Cave included riparian forest and open woodland containing many plant species. However, those plants were almost absent from the archaeological deposits. The people using the cave instead selected grasses that grew relatively close to its entrance.

“The phytoliths found in Cloggs Cave were from different parts of grasses, including stems, leaves, flowers and roots, indicating that the entire grass was introduced, including the inedible parts,” Grono said.

Evidence of ritual burning over thousands of years

Approximately 18% of the phytoliths showed signs of combustion or dissolution. These altered plant remains appeared throughout the dated deposits, suggesting that people repeatedly transported plants into the cave and burned them over a period of approximately 25,000 years.

The discovery supports other archaeological evidence indicating that Cloggs Cave was a site of long-term ritual activity rather than an ordinary living area.

Professor Bruno David of Monash University, who led the excavations in conjunction with the Gunaikurnai Land and Waters Corporation, said the burning was consistent with traditional Gunaikurnai practices involving ashes in magic and rituals. Ashes were also used to track the footprints of human intruders, including spiritual beings.

Other macrobotanical evidence, including wooden sticks coated with fat and trimmed Casuarina trees, was also found. These discoveries in deeper, older deposits indicate that additional rituals involving woody plants were performed at the site.