Dwarven Sphere (Skyrim)

Centurion Spheres are machines that serve as sentries or guards in Dwarven ruins and other select areas.

Their loot consists of Dwarven metal parts and various level soul gems.

Behavior
These enemies 'roll' around as a protected sphere. Once they sense a threat, they come out of their spheres and search for nearby enemies.

If they find the threat they'll attack it with either Crossbow or Sword.

Tactics
The Centurion Spheres are fast, and will easily take-down lower level players (specifically mages and warriors who may try and keep a close-mid range). The often charge as their main attack.

A fully charged "Unrelenting Force" shout will cause it to stagger. If you turn invisible and sneak up to it with the Blade of Woe or an enchanted battleaxe and If you are quick and stab or slash straight away at them they will lose health quickly (special attacks are not very useful except against steam centurions) they are weak aginst drain health, fire, and shock magic.

One tactic that seems to work on them is using the "Marked for Death " shout and any combination of non magic weapons, this extremely weakens the spheres armor and capability to defend against physical attacks.

Another good tactic for those with decent archery is to turn invisible or sneak up on the sphere and hit it using the 3.0x bow damage while sneaking perk to severely weaken it, and it should take only one or two shots afterwards to kill it. Using range ensures avoidance of the resistance to magic and the damaging counterblows.

Yet another useful tactic is a sword in one hand and "Fast healing " in the other.

Source
The Elder Scrolls V: Official Skyrim Game Guide