A sophisticated bronze- and copper-casting tradition centred on three excavated sites (Igbo Richard, Igbo Isaiah, Igbo Jonah) at Igbo-Ukwu, Anambra State — the oldest known lost-wax bronze casting in West Africa, predating Ife and Benin. Over 700 high-quality metal artifacts (ritual vessels, regalia, staff ornaments) plus ~165,000 imported glass/carnelian beads point to a wealthy, hierarchically organized society with long-distance trade links reaching North Africa and Egypt via the Niger bend.
The archaeological horizon appears to end by the 11th century with no clear successor casting tradition at the site itself; the Igbo-Ukwu bronzes are sometimes linked culturally (not politically) to the later Kingdom of Nri, a few miles away.
By the excavator himself (1959/1964 digs); the accessible companion to his full two-volume 1970 excavation report, specific to this site.