Exhibit Antiques has dated this piece to the Before 1700 period.
Beautiful flaking iridescence.
Spherical body with a flattened base and slightly concave bottom; a distinct tooled constriction between the body and cylindrical neck. Plain, knocked-off vertical rim.

Date & Origin
Roman. Late Imperial Era, 3rd - 4th century CE.
Condition
Layers of iridescent flaking encrustations with further iridescence to the weathered glass surface.
Dimensions
Height: 6.8cm Diameter: 5cm

View documented examples in chronological order here:
2nd - 4th century AD: https://ancientglass.wordpress.com/2012/05/30/roman-spherical-bottle/
3rd - 4th century AD: https://www.ktb.gov.tr/EN-120323/late-roman-imperial-period-glassware.html
4th century AD: https://www.metmuseum.org/art/collection/search/239644
Exhibit Antiques has dated this piece to the Before 1700 period.
Specialists in 18th & 19th century antique glass
You can view the stock and full dealer information on the Exhibit Antiques Profile Page