From 1600 to 1750 the Tāmaki tribes terraced the volcanic cones, building "pā". Across the isthmus they developed 2,000 hectares of kumara (sweet potato) gardens. At the peak of prosperity in 1750, the population numbered tens of thousands. It was pre-European New Zealand's most wealthy and populous area. However, from the early 18th century the Ngāti Pāoa people edged their way into the Hauraki Gulf and as far north as Mahurangi. Between 1740 and 1750 Ngāti Whātua-o-Kaipara moved south, invading the isthmus and killing Kiwi Tāmaki, paramount chief of Wai-o-Hua. They then took his last "pā" at Mangere. Ngāti Whātua secured their dominance of the isthmus by intermarrying with Ngā Oho, descendants of the Wai-o-Hua. There followed a period of cautious peace in which Ngāti Pāoa's conflict with Ngāpuhi tribes in the north made the Tāmaki tribes vulnerable to attack.