Jim Davila has picked up a discussion about ancient testimony to the earth’s spherical shape. Cicero also, by way of his Stoic character Balbus, comments to this effect, saying,
[T]he sea, which is above the earth, tends still toward the earth’s centre, and so is itself shaped in conformity to the globe of the earth and nowhere spills or overflows. (171; italics added)
So, the Stoics, and perhaps Cicero, also would have acknowledged a spherical earth “before their time” (75, 238).
Yes, I’m sure they knew there was a spherical earth. The iconography of a spherical globe in Roman art and propaganda was quite pervasive in the first century and earlier. I’ve written briefly on it here: http://wp.me/p5gCf-O. Also check out this recent post by a new blogger http://www.richardoster.com/2011/09/geopolitical-jesus-emperor-hadrian.html