At the start of the dynasty, under King Nebka, Memphis became the permanent residence. Djoser, his successor, is considered to be the most important ruler of this dynasty. He is called the founder of the Old Kingdom. His tomb is well known: the Step Pyramid at Saqqara, built by Imhotep. The next king was Sekhemkhet. His tomb was begun near that of Djoser, but never completed. In the days of these kings the first mines in Sinai were opened up for copper and turquoise. King Nebka and his successors are represented in reliefs near the mines of Wadi Maghara. After the short reign of Khaba (unfinished step pyramid near Zawayet el-Aryan to the north of Memphis), a struggle for the throne began between various pretenders. Huni eventually emerged the victor. He built a fortress on Elephantine island near the 1st cataract and extracted granite from the Aswan quarries for statues and the construction of his mortuary temple. The pyramid of Maidum was possibly built for him.