Construction of the heiau began after Kamehameha's return from Maui in 1790. The scale was enormous: the finished platform measured roughly 224 by 100 feet, built of waterworn basalt and lava rock without mortar. According to tradition, the stones were passed hand to hand along a human chain stretching miles, from Pololu Valley on the island's northern tip to the construction site at Kawaihae. Thousands of people labored on the project. Among Kamehameha's allies during this period were two Europeans who had come into his service through violent circumstances. Isaac Davis had survived the capture of the American trading vessel Fair American at Olowalu in 1790, and a stranded British sailor named John Young had been detained on the island. Both became military advisors, instructing Kamehameha's warriors in the use of muskets and mounting cannons onto double-hulled war canoes. Young built a house and ranch near the heiau, a site now preserved within the national park.

In the summer of 1791, the temple was complete. Kamehameha needed a final offering to consecrate it, and he turned to his cousin and rival Keoua Kuahuula, who still controlled the eastern side of the Big Island. Kamehameha summoned Keoua under the guise of a peace treaty. Why Keoua accepted the invitation remains one of Hawaiian history's unanswered questions. Perhaps he was demoralized by the loss of many warriors in the Battle of Hilo and a devastating volcanic eruption in 1790 that had killed members of his army. One tradition holds that Keoua, understanding what awaited him, deliberately mutilated himself before arriving -- an act meant to defile the sacrifice and deny Kamehameha the spiritual power the offering was supposed to confer. Regardless, Keoua was killed at Kawaihae, and his body became the consecrating sacrifice of Pu'ukohola Heiau.

Before the temple was even finished, Kamehameha's growing power drew a preemptive strike. Chiefs from other islands, alarmed by reports of his army and his European advisors, joined forces and attempted an invasion from the northeast. Davis and Young had drilled Kamehameha's warriors in Western-style warfare and fitted double-hulled canoes with cannon. The invading fleet, armed with traditional weapons, was no match. The battle, known as Kepuwahaulaula -- meaning "red-mouthed gun" -- took place just north of Waipio Valley. The invaders were repelled decisively. It was an early demonstration of the military advantage that European weaponry would confer on Hawaiian chiefs who acquired it, and it announced that Kamehameha's ambitions now extended beyond the Big Island to the entire archipelago.

Today the National Park Service operates a visitor center at the site, and an interpretive trail leads from the center to the heiau's massive stone platform. But visitors cannot enter the temple itself. The restriction is not bureaucratic -- it is spiritual. Bones are believed to still lie within the structure, and the site retains its sacred significance. About 170 feet west of Pu'ukohola stands the older Mailekini Heiau, which John Young later converted into a fort to guard the harbor. Just offshore lies Hale o Kapuni, a submerged structure once dedicated to sharks, where a stone post on the shore once marked the viewing spot for their ritual feeding. Across the bay, the modern harbor of Kawaihae handles commercial shipping and pleasure boats. The heiau was designated a National Historic Landmark on December 29, 1962, and listed on the National Register of Historic Places in 1966 -- formal recognition of a place whose significance was established two centuries earlier, when a priest's prophecy and a warrior's ambition reshaped the Pacific.