Check out Robin Lane Fox for Graeco-Roman history, he is a reknown historian on this era. Adrian Goldsworthy wrote some good works too (Fall of Rome) and particularly on the fall of Rome side, check out Peter Heather & Chris Wickham. I loved the Hellenistic World by Tarn & Griffith (ed.), but it is by now in some fields somewhat outdated, a more modern work on the Hellenistic world is Age of Conquests by Angelos Chianotis.