5 Dimensions + 3 BC

Imagine that the events of Poul Anderson's fictional narratives occur in different parts of a single five-dimensional space-time. Each particular sequence of events has the usual three spatial dimensions and one temporal dimension. Additionally, the sequences are separated by a fifth dimension which is either a fourth spatial dimension, a second temporal dimension or a third kind of dimension. The fifth dimension is traversed by multiversal travellers and by guests of the Old Phoenix.

Each sequence of events is a single timeline. Thus, there are multiple pasts and futures. In some cases, we are shown very remote futures. When we say that three of Anderson's novels are set BC, we do not necessarily mean that they are set in the BC period of the same timeline. In fact, they are almost certainly not.

Conan The Rebel is heroic fantasy set in a remote fictional past.

The Dancer From Atlantis is historical sf/time travel fiction set in Atlantis.

The Golden Slave is historical fiction set in 100 BC.

Conan... is the earliest.