Warmest thanks for this message from Professor Sarah Bond, University of Iowa:
As many of you know, the Mapbox servers previously used for hosting the AWMC maptiles have been down for a number of months as we figured out a better way for them to be hosted and funded. Digital preservation is one of the hardest parts of any DH project. This has caused much disruption with digital projects that rely on these as maptiles as base maps for interactive, spatial components. As such, we want to announce that the AWMC maptiles have been migrated to a server at the University of Iowa libraries within The Digital Scholarship and Publishing Studio. You can download or use the maptiles in a number of formats: http://cawm.lib.uiowa.edu/index.html 
Below you can see more about the official licensing (still a CC BY 4.0) and attribution. We are calling this spinoff CAWM (the Consortium of Ancient World Mappers), but it is still made up of many former heads of the AWMC (e.g. Ryan Horne, Richard Talbert), Pleiades editors (e.g. me) and Pelagios partners. We hope these freely available maptiles will be used widely and that the stability of their provision will be relied upon as you rebuild or create new digital projects with spatial aspects. http://cawm.lib.uiowa.edu/#tiles/ol3
In addition to the digital tiles, we are working on new versions of Antiquity à-la-carte to help people to make their own accurate maps for articles and books. In the meantime the older version is still up and able to be used to create maps for analog publications: http://awmc.unc.edu/wordpress/alacarte/
We are all excited about this new venture with amazing partners, and have huge gratitude for the original AWMC mapmakers who created these tiles in 2014.
Questions about these maptiles or future pedagogy workshops with Pelagios on how to use them can be directed at me. I also want to give a huge thanks to Jay Bowen, our GIS specialist at the Studio, for his aid in coming up with a solution for hosting the maptiles from Iowa.