Goa'uld cannon tower
From The Stargate Omnipedia
A massive multi-story arm which houses a Jaffa soldier and Goa'uld cannon at the top. The tower can burst from beneath the surface to maintain the element of surprise and corral invaders, cleanly decimating them where they stand. Targeting sensors are capable of locking on to stationary targets with ease, but it becomes increasingly difficult for the sensors if the target is evasive.
KEY EPISODE
Into the Fire - Two cannon towers protrude from the ground, surrounding several SG units as they search for the missing SG-1.