Construction of a new and even more formidable defence line began 25 km south of Ngāruawāhia, soon after the fall of Rangiriri. The line included fortifications at Pikopiko and Rangiatea and was centred on
Paterangi, its largest
pā, and was designed to block the main approaches to the agriculturally rich
Rangiaowhia district, east of
Te Awamutu, a major economic base, trading with Auckland, San Francisco and Melbourne, and a supply centre of the Kingite tribes. By the end of January 1864 the line had become the largest system of Māori fortifications of the land wars, consisting of at least four large
pā spaced about 8 km apart, each of which included complex sets of entrenchments and parapets. The defence system, which included two cannons, was manned by a force of between 1200 and 2000 men from a dozen major Waikato
iwi. Two weeks after capturing Ngāruawāhia, Cameron's 3000-strong striking force, protected by another 4000 men, began slowly and cautiously advancing south. In late January Cameron moved his army headquarters to
Te Rore, about 5 km from Paterangi, with an advance camp for 600 men positioned just 1.2 km from the
pā, from where they judged the defences were "immensely strong". A new supply line was established from Auckland, using boats to
Raglan and packhorses across the ranges to meet steamers on the
Waipā River. But a further advance into the heart of Kingitanga territory was delayed when the
Avon—one of the most important components of the transport and supply system—accidentally sank in the Waipa on 8 February. A significant engagement took place on 11 February when an assault party from Paterangi ambushed a group of soldiers bathing in a loop of the Mangapiki Stream at Waiari, near the British forward position. Two hundred of Cameron's troops, with the Forest Rangers, became involved in a running battle with the attackers and killed an estimated 41 Māori, losing six of their own men. There were about 200 Ngati-Apakura and Ngati-Hinetu people at Rangiaowhia, supplying food to the garrisons at Paterangi
pā. Cameron, meanwhile, was attracting sharp criticism from both the colonist press and Grey himself and at least one attempted to surrender, but was murdered by troops ignoring their orders. Women were raped and killed in front of children. About a dozen houses were burned down. The British claimed they killed 12 Māori, including two chiefs, and took 30 prisoners. Their own losses totaled five, including several officers. When Cameron's forces returned to Te Awamutu, the men of Rangiaowhia abandoned Paterangi, Pikopiko, and Rangiatea
pā to defend their families and began rapidly digging a new trench on the crest of a ridge at Hairini, cutting the route between Te Awamutu and Rangiaowhia. The wife and two daughters of
Kereopa Te Rau were killed in the attack, and his sister was killed in defence of the Hairini line a few days later.
Colonel Marmaduke Nixon, who had led the Rangiaowhia cavalry charge, was mortally wounded. His remains are buried at the Nixon memorial in
Ōtāhuhu, Auckland. There were no memorials to the victims of Rangiaowhia until the 150th anniversary was commemorated in 2014 with the unveiling of a plaque. ==Ōrākau==