Color & Markings
Once known for their elaborately carved, exquisitely maintained battle armor, the "warrior reptile" Sill are now most commonly known for their monastic robes.
Reproduction & Development
The Sill reproduce sexually, generating a nested brood of 1-3 offstring. Once hatched, these offspring would've traditionally been raised within an extended family, and schooled for free at the local house of education, run by The Hold.
Schooling would've been followed by military training, then by a decade of service, and finally by a caste-appropriate occupation.
Omnivorous, but with a deathly allergy to pollinating fruits.
The Sill originally had three languages: A common tongue used for friendship and familial matters, a logistics tongue for military and tradecraft, and an imperial tongue, used by or with the royal family of the Hold. Today, of course, only the imperial tongue survives with the Monks of Yanta.
For tens of thousands of years, The Hold of the Sill followed a fixed caste system. But early in its expansionist years, The Hold's caste system "stretched," and began allowing for upward mobility within one's caste. This mobility was made possible by the constantly expanding territories of The Hold. Any young Sill could now find military and financial success out among the colonies, and return to the core worlds to bask in wealth.
The Hold lasted between 20 and 25,000 years, in various incarnations, and is generally considered the greatest empire the galaxy has ever produced. By technologies now lost, The Hold stood astride many lightyears of the Milky Way, and was resplendent with riches, art, and culture. Even now, when the grand architecture of The Hold is but a crumbling memory, hundreds of species still feel a lingering impact from art, culture, and literature.
After eons of rule, the complete fall of The Hold was quick -- taking only 10-15 years. And it wasn't brought down by armies, or plague, or a massive gamma-ray burst. It was brought down by a slim, 15-page book: The religious teachings of the Prophet Ekka. Ekka taught a simple step-by-step way for The Sill to to align their mind to what she called "organic energy." And the simple fact is, it worked. The technique was transformative for The Sill. Ekka's teaching brought an overwhelming sense of peace, well-being, and interconnectedness with the universe. Many Sill lost all desire to reproduce. As was true with other bodily functions like sleeping and eating, the desire to reproduce could only be generated with great mental effort and concentration. As such, within two generations, an empire of 250 billion was reduced to 3 million: The remnant Monks of Yanta.
Interaction with Humans
For many species, The Sill were their first contact with alien life. As such, you can find repeated references in the histories of ancient Veeta, Kayntanna, Finntesk, the Fillipods of Tesskil, and hundreds of others. But Earth remained blissfully unaware of The Sill until the early 2300's. As such, humanity's picture of the Sill is colored very differently than that of most other species. For others, The Sill were a massive, conquering, trading empire that straddled space lanes in all directions... only to suddenly turn inward on a religious path. But for humans, The Sill are nothing more than a boring monastic community, with not much to offer. And who frankly need to wash more.