Dashan Island sits 28 nautical miles from the coast of Lianyungang, a major port city in Jiangsu Province. At just 0.115 square kilometers, it would take only a few minutes to walk its entire perimeter. The island belongs to the Qiansan Islands group, a scattered chain of small islets and rocks that dot the waters off the northern Jiangsu coast. From above, it appears as little more than a dark smudge against the grey-blue waters of the East China Sea, unremarkable to the casual observer but precisely plotted on every official Chinese maritime chart.

On May 15, 1996, the Chinese government issued a formal declaration establishing the baselines of its territorial sea. These baselines are the legal starting points from which a nation measures its maritime zones, including the twelve-nautical-mile territorial sea and the two-hundred-nautical-mile exclusive economic zone. Dashan Island was named as one of these critical reference points. A decade later, in 2006, the PLA completed a project to install territorial sea steles on ten such baseline islands in the East China Sea, physically marking the legal boundaries with engraved stone markers. Each stele transforms an abstract line on a map into a tangible assertion of sovereignty.

Dashan Island belongs to a category of features that maritime lawyers and diplomats spend careers debating. Under the United Nations Convention on the Law of the Sea, whether a feature qualifies as an island, a rock, or a low-tide elevation determines how much ocean a nation can claim around it. Dashan Island is part of a network of similar baseline points stretching along China's coast, from the Bohai Sea in the north to the South China Sea far to the south. Each point anchors a line, and each line shapes the boundary between national waters and international seas. For an island smaller than a city block, Dashan carries an outsized role in one of the most consequential legal frameworks governing the world's oceans.

The waters around Dashan Island are typical of the shallow, nutrient-rich East China Sea shelf. Fishing boats from Lianyungang and the surrounding coastline work these waters regularly, pulling in catches that have sustained coastal communities for centuries. The Qiansan Islands, scattered like stepping stones toward the open ocean, have long served as navigation landmarks for sailors threading their way along the Jiangsu coast. Dashan itself is not inhabited, and no permanent structures stand on it beyond the baseline stele. It remains, as it likely has been for millennia, a lonely outcrop of rock visited mostly by seabirds and the occasional patrol vessel confirming that the stone marker still stands.