African Sigillata 1 Base 5

Base from medium-sized closed form.

Disk base with curved outer face with slight groove at upper edge and groove on underside close to edge; steep lower wall; slip on exterior surface only. 

Closest comparandum is Hayes Form 161 n. 1/Atlante I XXII.3 table amphora.  Context and fabric of sole example suggests may be base of African Sigillata 1 Form 18.