Complex sentence: Indeed Seneca wrote that around 61 AD Nero sent some legionaries to the city of Meroe in Nubia in order to explore all the Nile southward from that capital, because he wanted to get information about Equatorial Africa and the possible richness of the area.
Split into simpler sentences: Indeed Seneca wrote that around 61 AD Nero sent some legionaries to the city of Meroe in Nubia in order to explore all the Nile southward from that capital. This expedition was done because he wanted to get information about Equatorial Africa and the possible richness of the area.