From Halopedia, the Halo wiki
Accompany other Forerunner machines and assist them with their tasks.
- "Stewards: These Sentinels accompany other Forerunner machines and assist them with their tasks, using a combination of support systems and offensive weaponry.The largest constructs are classified as strato-sentinels, taking the roles of grand builders and overseeing architects for major Forerunner works. Those used in military applications were often classified as weapon-ships, capable of being fitted with naval-scale ordnance and defensive systems."
- — Jeff Easterling
The upper section of a Steward is vast and wide, with two "arms". Three glowing eye-like lights are installed on the front of each Sentinel with two "claws" below it. The lower section is lined with four mechanical, tentacle-like "legs". Three glowing eye-like lights are installed on the front of each Sentinel.
The Stewards are fitted with a combination of support systems and offensive weaponry.
Concept art of the Strato-Sentinels, handed out at Outpost Discovery as prints for VIPs. 
Strato-Sentinel concept art, with a comparison of older Halo 3 concept art for reference.
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