Ship's cannonball found by Transmission Gully road workers
Workers on the massive Transmission Gully road project have unearthed what is believed to be a mid-19th century ship's cannonball.
The 53kg sphere is about 25cm in diameter and was found in the headwaters of the Horokiri Stream site.
Project archaeologist Mary O'Keeffe said the ball had "the exact dimensions of balls used in huge cannons mounted on ships around the mid-19th century".
"How it ended up in the creek is a big mystery."
Initial speculation had the find dating as far back as 1846, when Crown troops attacked the pa of Ngati Toa leader Te Rangihaeata and his people at Matai Taua (Pauatahanui) and Battle Hill in the valley.
"But the cannonball was found some 2km from Battle Hill and anyway there are detailed records of the guns used there. They fired balls only around a tenth of the weight of this one," O'Keeffe said.
An exclusion zone was set up when the ball was found, police and an army bomb disposal unit were called in as a precaution, and Ngati Toa iwi was notified.
Strict protocols also apply to suspected pre-European sites. Machinery operators are instructed to stop work immediately if an unusual item is found or even if a patch of ground looks different to surrounding areas.
O'Keeffe said a half-finished adze that may date back to the 16th century had been found near Mackays Crossing.
The cannonball is likely to end up in Pataka Museum at Porirua, while Ngati Toa would be consulted about the adze.