Lejja is a community of 33 villages in Enugu State, southeastern Nigeria. Lejja is mainly inhabited by the Igbo people and is located on the edge of the Benue Plateau, which has rich laterite and basalt resources. Archaeological evidence of iron smelting in Lejja dates back to 2000 BC, making it one of the earliest and most important iron smelting sites in sub-Saharan Africa.

Otobo Ugwu square in the Dunoka village is a famous iron smelting site (6°45′5.37″N 7°21′21.65″E / 6.7514917°N 7.3560139°E / 6.7514917; 7.3560139), which contains more than 800 cylindrical slag blocks, each weighing 34 to 57 kilograms. Most of the religious customs related to the monument in the square are associated with iron smelting activities, which together form an important intangible cultural heritage of Lejja in terms of politics, economy, judiciary, medicine, gender relations and other aspects. Archaeologists have discovered multiple ironmaking, residential and ritual sites in the Lejja area, providing historical evidence for understanding ancient ironmaking technology, religious customs and socio-political structures.

As one of the important sites for understanding the origins of ironmaking in Africa, Lejja's cultural heritage is increasingly threatened by modern urban development and cultural changes.^{[citation needed]}

Lejja is located in Nsukka, Enugu State, southeastern Nigeria, and is a group of 33 villages (including Dunoka, Amaowoko, and Obka). Lejja is part of the "Omabe" cultural group, which also includes Obimo and Opi, and Lejja is the "Onyishi Omabe (Chief of the Omabe)".^{[citation needed]} Lejja is divided into three main regions: Ejuona, Uwani, and Ekaibute (also known as Akibute), and is divided into two political zones: Ejuona (Uwani) and Ekaibute. According to the 2006 Nigerian census, Lejja has a population of over 80,000.

Lejja is located on the edge of the Benue Plateau, the terrain is mainly hills and valleys. The rich laterite and basalt resources provide the geographical basis for the early iron smelting in Lejja.

The archaeological survey of Lejja began in the late 20th century, which was jointly conducted by Nigerian universities and international scholars. Experts used cross-sectional surveys and fixed-point excavation methods to identify 16 representative archaeological sites in 13 villages. The archaeological team divided these sites into three types: iron smelting sites, residential sites and sacrificial sites. According to radiocarbon dating data, the iron smelting activities in Lejja can be traced back to 2000 BC and continued until the 15th century AD, indicating that the Lejja site is one of the earliest iron sites in the current Nigerian archaeological record.

Lejja is one of the earliest and best-preserved archaeological sites of iron smelting in sub-Saharan Africa. The iron smelting sites in the region are mainly concentrated in and around village squares, including Amaovoko, Dunuoka, Amaebo-Attamah, Obukpa and Umuezeoda. Several archaeological surveys conducted between 2006 and 2024 confirmed that large-scale iron smelting activities were carried out in Lejja.

Otobo Ugwu (term for a ceremonial square) in the Dunoka village is the main iron smelting site, which is mainly composed of more than 800 cylindrical slag. Slag cylinders, aggregate slag, tuyere and furnace walls are direct evidence of the early iron smelting stage at Nsukka. Slag cylinders are formed by high-temperature smelting, discharged from the furnace through tuyere (connecting pipe), and then naturally cooled and solidified in a clay-lined pit. These cylindrical slags are about 31–56 cm in diameter, with an average density of 3.89 g/cm3, and the average weight of intact slag is between 34–57 kg.