The cult in its current form dates to the Second Age, but is of great importance in Caladraland, and also found among the Ditali.
Twins are a matter of great magical significance in Glorantha – each of the Runic polarities can be thought of as manifestation of the cosmic Twins – and you see that a lot in the Earth Religion (Asrelia-Ty Kora Tek, Ernalda-Maran Gor, Babeester Gor-Voria). But I think Caladra and Aurelion are the most important cult where both twins are worshiped together in a single cult.
The Twin Gods combine Heat and Earth, Fertility and Harmony. They are crafters, miners, and musicians – the lyre is their instrument.
Veskarthan is just an old Kethaelan name for Lodril. After a few centuries of God Learner domination, Lodril might be the popular name. He’s the big volcano god. About 11% of the population in Caladraland follow Lodrill. The Orlanth cult is about the same size as Lodril in Caladraland (10% of the population).
Caladra and Aurelion – the Twin Gods – are actually more popular in Caladraland than Lodril – 20% of the population follow the Twins, and twins are a huge deal in Caladraland.
The most popular cult in Caladraland is…. Ernalda with some 35% of the population. She is the older sister of the Twins and worshiped as the daughter of Lodril.