Ha'amonga 'a Maui — the "Burden of the God Maui" — is an ancient coral trilithon standing at Niutoua, 32 km east of Nuku'alofa. Two upright pillars support a central lintel weighing more than 8,900 kilos, forming a gateway thought to mark the entrance to an old royal compound. The structure now stands in an archaeological reserve.
Nearby is a large upright slab, said to be the backrest of the Tu'i Tonga who reigned around 1200 AD. The real purpose of the Ha'amonga has been debated for centuries — comparisons to Stonehenge are inevitable. In 1967, King Taufa'ahau Tupou IV proposed that a V-shaped notch cut into the top of the lintel was used for ancient astronomical observations. Tests confirmed that the notch aligns with the position of the rising sun on the solstices, marking the shortest and longest days of the year. In 1972, the king declared Ha'amonga a protected national park.