It's a cannon. I've actually been to visit the museum in Gonzales, and the cannon is quite small. We walked around the area where the skirmishes took place.
If you have the time, do a search for "Battle of Gonzales": https://en.wikipedia.org/wiki/Battle_of_Gonzales
I did look it up. COME AND TAKE IT.
MOST interesting bit of history. "Although the skirmish had little military significance, it marked a clear break between the colonists and the Mexican government and is considered to have been the start of the Texas Revolution."
Thanks.