They believed in Yahvo the Maker whom they honored in the Feast of the Maker. They also believed in prophets. Among their traditions was the Regeltavok of Oorpah, where the arrival of the Great King through the King's Arch was prophecised, sent by Yahvo to guide the Ronay.
They also possessed "the Art", which was believed by the D'ni to have been delivered to them by the Maker. There are many legends about the origin of the Art, but all are conflicting. The Art was a technology that allowed them to travel to other dimensions (Ages) which they described in special Descriptive Books. Whenever the Ronay explored/surveyed a new Age, they established the Great Zero on a prominent natural landmark, from which a line was drawn (usually toward magnetic north or another prominent landmark), to aid in exploration, navigation, construction, etc.
The Ronay were ruled by a King. Their society was composed of 18 Guilds. One of them was the Guild of Writers which possessed the knowledge of the Art. One entered a Guild normally at age 5. They Guilds had flexible rules to accomodate the needs of the time. However they were tainted by competitiveness between them, and they were often focusing on their facilities that their duties to Yahvo and the people. The usage of the Art was motivated by humble purposes. Grand Master Ri'neref of the Writers criticised the views of the King and the Guilds.
Ri'neref was asked by his Grand Master to write an Age, home of an uncivilized race that could be used for their own purposes. Ri'neref questioned the morality of such an action and after much debating he left the Guild, sparking controversy among the Ronay. Meanwhile Ri'neref knew the truth that Garternay's sun was dying and would eventually cause a rapid decrease in temperature, making their world uninhabitable. Eventually the fact was made public and the people had to migrate to other worlds.
The majority of Ronay left Garternay to a new home world called Terahnee ("new tree"), but the King allowed a few small groups to split away. Ri'neref managed to attract a few thousand loyal Ronay who respected him and convinced them to follow him to his Age, which happened to be Earth. Those were the D'ni (meaning "New Beginning"). Nothing is known about the other groups.