Can cows swim?
I shot an arrow into the air, it fell to earth with a bang over there.
Tiber River/Crossbow (a.d. IX Kal. Sep.)
You'll see reports that someone has flooded the cattle market down by the Tiber. Go down to the river by following the street to the left of the Temple of Saturn until you hit some wooden machinery (to the right of which is where Gordian's temple is being built -- you can check on its progress periodically). Click on the machinery and continue to the river steps. To the left is the flooded cattle market mentioned in the scrolls and Acta -- playing with the animals does nothing important, but it's fun. Downstairs, you'll see a bunch of junk and a box marked "Explosive." Go back up the stairs and continue to the bridge; make a left. On the left-hand railing is a crossbow. Click on the wire thing you found in the Baths and it will attach itself to the crossbow. Click on one of the arrows to "load" it. Watch the wind indicator to the right, and try to fire at the spot near the temple in the distance (where the junk is). Keep trying until there's an explosion; a wooden horse, a "water key", and a scroll come flying down.