The Sil’ess were a reptilian race that inhabited one or more iterations of Mars, and whose artifacts have been discovered across the Splinterzone. They were apparently well versed in magic and technology, and devised crystalline energy weapons and devices. The stories of their empire have influenced some of the reptilian descendants of the CAN Reptile House, and the association of the Sil’ess with dangerous and forbidden lore has given Sil’ess artifacts a sinister reputation.

According to Steig, the Sil’ess culture was originally polytheistic, until the religion of the The Dark Mother arose and sought to exterminate the other sects. Only a group called the Red Cadre posed a threat to the servants of the Dark Mother, who named themselves the Apep, and the resultant war led to the Apep uncovering the secrets of mouldstone.

The carved doors of Riffkin’s sanctum appeared to depict one Sil’ess carrying a mouldstone casket, facing another carrying a cube. The tapestry seemed to depict the religious war, with both sides fielding strange automatons, and the Red Cadre centered around a curious egg-like object.