It's difficult to choose the best academic textbook on ancient history since there are many excellent options focusing on various time periods, geographical regions, and civilizations. However, one widely recommended and comprehensive textbook is "The Oxford Handbook of Ancient History" edited by Brian Campbell. This book provides a solid overview of ancient history by combining different disciplines (history, archaeology, and art) and covering various civilizations such as Egypt, Mesopotamia, Greece, and Rome. It is suitable for both beginners and experts, as it offers a wide range of topics and approaches to the field. Keep in mind that depending on your specific topic of interest, other textbooks might be more suitable.