The story of Kasugayama's survival begins with religion. The forested slopes of Mount Kasuga served as the sacred backdrop -- the chinju no mori, or shrine forest -- for Kasuga-taisha, the grand shrine established in 768 CE as the spiritual seat of the powerful Fujiwara clan. In Shinto belief, forests surrounding shrines are dwelling places of the kami, and to disturb them invites divine displeasure. Emperor Ninmyo formalized this reverence in 841, issuing an imperial prohibition on logging and hunting throughout the mountain. The decree held through the upheavals of the Kamakura, Muromachi, and Edo periods, through civil wars and modernization, through the Meiji Restoration that dissolved so many old traditions. Japan's government designated the forest a Natural Monument in 1924 and elevated it to Special Natural Monument status in 1955 under the Law for the Protection of Cultural Properties. In 1998, UNESCO inscribed it as part of the Historic Monuments of Ancient Nara World Heritage Site.

The result of twelve centuries of protection is an ecosystem of extraordinary richness. The forest contains 175 species of trees, including massive camphor laurels, chinquapin oaks, and Japanese cedars whose trunks have grown thick enough that several people cannot link arms around them. More than 800 plant species carpet the forest floor and climb its slopes. Sixty species of birds nest among the branches, including the endangered ruddy kingfisher. Researchers have cataloged 1,180 species of insects here, along with the clouded salamander and the forest green tree frog. Mount Kasuga itself rises to 498 meters, a modest summit, but its ecological significance is immense. The forest is essentially a control group -- a sample of what the Kansai region's broadleaf evergreen forests looked like before centuries of logging, farming, and urban expansion transformed the landscape. Scientists study Kasugayama to understand how Japanese ecosystems function when left to their own rhythms.

The sacred deer of Nara are inseparable from the forest's story. In Shinto tradition, the kami Takemikazuchi rode a white deer from Kashima Shrine in eastern Japan to Mount Kasuga when the capital was established at Nara. Ever since, the deer that roam Nara Park and the forest slopes have been regarded as divine messengers. For centuries, harming a deer in Nara was a capital offense. Today more than a thousand sika deer wander freely between the shrine grounds, the open parkland, and the forest edge. They are wild animals, not domesticated, but they have lost their fear of humans through generations of coexistence. In the forest, away from the tourist crowds offering shika senbei crackers, the deer move through the undergrowth with a quieter purpose, browsing on the same vegetation their ancestors have eaten for a millennium. Their grazing shapes the forest floor, keeping certain plant species in check and allowing others to flourish -- an ecological role as old as the imperial decree that protects the trees above them.

Several hiking trails cross the forest, ranging from easy loops near the shrine to steeper paths ascending toward the ridgeline. The Kasugayama trail starts behind Kasuga-taisha, following stone-paved paths past moss-covered lanterns before entering the canopy. The air temperature drops noticeably under the old-growth cover. Sunlight filters through layers of leaves, dappling fern-covered slopes in green-gold light. The forest feels ancient in a way that cultivated Japanese gardens -- designed to evoke nature -- cannot replicate: this is the real thing, unmanicured and uncurated. The trail eventually connects to paths leading to the summit of Mount Wakakusa, where the view opens across Nara's urban grid to the mountains of Yoshino. Every January, the dry grass of Wakakusa's open slopes is set ablaze in the Yamayaki festival, a controlled burn that lights the night sky orange. The contrast is deliberate -- the wild fire on the open hill, the ancient forest behind it, untouched and untouchable.