By 1609, the Dutch East India Company had been trading in the Bandas for a decade, but trading was not the same as controlling. The Bandanese played European merchants against one another, selling nutmeg to the highest bidder. The VOC wanted exclusivity. On April 25, Admiral Pieter Willemsz Verhoeff arrived with a fleet and sent 750 soldiers ashore to begin construction on the abandoned Portuguese foundations. The Bandanese understood what a fort meant: the end of free trade, the beginning of monopoly. In late May, local chieftains invited Verhoeff and two of his officers to negotiate on the beach, then led them into the woods. It was an ambush. Verhoeff and 45 of his men were killed. The Dutch soldiers retaliated by burning Bandanese villages and destroying their boats, and by August a peace treaty favorable to the Dutch was signed. Fort Nassau would be completed.

The fort that rose on the shore of Banda Neira was a large four-bastioned quadrilateral, positioned to command the channel between Banda Neira and Banda Besar. It served as the principal administrative and military headquarters of the VOC in the Banda Islands, the nerve center from which the Dutch managed their nutmeg monopoly. From Fort Nassau, colonial administrators coordinated the operations of satellite fortifications across the archipelago: Forts Hollandia and Concordia on Banda Besar, and Fort Revenge on the island of Ai. The spice that justified all this military infrastructure was staggeringly valuable. Each time nutmeg changed hands along the trade route from the Bandas to European markets, its price doubled. The fort existed for one reason: to ensure that every gram of that nutmeg passed through Dutch hands first.

Fort Nassau's fatal weakness was geographic. It sat at the foot of a hill, and anyone who held the hilltop held a commanding position over the fort below. The Dutch recognized this vulnerability almost immediately. In 1611, just two years after Nassau's completion, Governor-General Pieter Both ordered a second fort built on the hill above it. That fort, named Belgica, would eventually be rebuilt into the striking pentagonal fortress that dominates Banda Neira's skyline today. Fort Belgica's five towers and angled bastions made Fort Nassau redundant as a defensive position, though Nassau continued to serve administrative functions. The relationship between the two forts became a kind of architectural hierarchy: Nassau handled the paperwork of empire while Belgica handled its defense.

The most devastating chapter in Fort Nassau's history unfolded in 1621. Governor-General Jan Pieterszoon Coen, determined to enforce the VOC's absolute monopoly, landed on the Banda Islands with over 1,600 soldiers and 250 Japanese mercenaries. What followed was systematic: the massacre, deportation, and enslavement of more than 90 percent of the Bandanese population. Forty-four local leaders were executed. Survivors were enslaved and sold. The VOC then imported enslaved laborers from Java to work the nutmeg plantations that the Bandanese had cultivated for generations. Fort Nassau stood at the center of this transformation, the administrative hub from which a free-trading society was dismantled and replaced with a slave-labor plantation system. The fort's walls witnessed the conversion of an entire people's homeland into a corporate commodity.

Today Fort Nassau is damaged and dilapidated. Two of its original four bastions remain standing, along with substantial sections of wall, but the fort has not received the restoration lavished on Fort Belgica up the hill. Visitors who climb the path to Belgica often pass Nassau's crumbling stonework without stopping. The contrast is fitting in a way the Dutch could not have anticipated: the fort built to project power now projects the impermanence of that power. The harbor it once commanded still serves Banda Neira, and the nutmeg trees still grow on the surrounding islands. What has vanished is the monopoly, the garrison, the enslaved workforce, and nearly all trace of the Bandanese civilization that existed before 1609. Fort Nassau's ruins are a reminder that the foundations of empire, like those Portuguese foundations the Dutch built upon, do not hold forever.