A couple of good rather technical articles on academia.edu:
Roman Policy on the Red Sea in the 2nd Century AD
https://www.academia.edu/14825342/Roman_Policy_on_the_Red_Sea_in_the_second_century_AD
Urban defences in the Northern Song dynasty (960-1127 AD)
https://www.academia.edu/14850996/Walls_and_Gates_Windows_and_Mirrors_Urban_Defences_Cultural_Memory_and_Security_Theatre_in_Song_Kaifeng
downloaded to read at lunchtime ;D
Thanks, Dave - both look quite interesting.