I've developed something on an obsession for ancient Roman glass, the existence and endurance of which feels quite miraculous to me, and I find it fantastically beautiful.  And while larger pieces are truly spectacular, a tiny bottle like this is equally thrilling to me, including for the fact that such a small thing with nearly 2000 years on it has found its way to me! I am no expert but I have been trying to look and learn. Based on the form and deep green color on this, I believe it likely dates to the 1st-3rd century AD, and I believe would have been used for medicine or perfume. 

2 5/16" t x 15/16" in diameter. No losses and a beautiful patina with areas of heavy encrustation and some irridescence. Stands upright on its own.