Zoku Thermae Romae

The year is 158 AD, and the Roman Empire thrives under the 20th year of Emperor Antoninus Pius's reign. Lucius, a Roman bathhouse architect, is now sixty years old and plagued with back pain. His wife Satsuki has mysteriously disappeared, his son, Marius, is beyond comprehension...and to top it off, he still has the Roman bathhouses to worry about!
(Source: MangaPlus)