Heinrich Köhler 384 Auction – Day 1 Single Lots: Europe and Colonies, Kingdom of Lombardy–Venetia – The "P.G." Collection

1880 (January 16), prepaid stampless cover to Constantinople, struck with blue Plovdiv c.d.s., straight-line FRANCO in blue below, with c.d.s. arrival backstamp (Jan 31), opening tear to back flap and some light creasing, else fine.
Note: responsibility for civil mails passed to Eastern Rumelian authorities in mid-1879, though adhesive stamps were not available until late 1880.