Picking up on the theme of the week...
The search function gives me answers to very specific questions, such as why the Romans didn't conquer the rest of the Nile, and why it wasn't feasible or practical for them to cross the Sahara.
That being said, I still wonder what they knew about South-Saharan Africa. Were they aware of the vast Rainforest / Jungle?
Also, the posts so far addressed the problems of venturing into jungle (Malaria, parasites) or across the desert, but what kept them from just sailing along the coast of the Red Sea
but what kept them from just sailing along the coast of the Red Sea
Nothing. They did sail down the coast of East Africa, and roman artifacts have been found in the Rufiji river delta in Tanzania. A Greek language document called the Peripleus of the Erythraen Sea written in 1st century Alexandria describes the coast of East Africa and mentions several ports, which modern scholars are debating the location of.
Here is a recent post I wrote that covers Roman and post-Roman contact with Africa, with links to sources.