An aqueduct - discoveries are being made even nowadays on this one: Trajan Æ Sestertius (103-111 A.D.) Rome Mint [IMP CAES NERVAE T]RAIANO A[VG GER DAC PM TRP COS V P P], laureate head right, slight drapery on left / [SPQR OPTIMO PRINCIPI, S-C, AQVA [TRAIANA] in ex. Aqua Traiana reclining left. RIC 463; BMCRE 873. (23.47 grams / 29 mm) Attribution Note: There are three RIC varieties of this coin. The most common seems to be RIC 463, so I went with that. See: RIC 607 and 608.