It was its closed, official nature that stood out about the practise of astronomy in China to early Western observers from Matteo Ricci to Joseph Needham—government control so strict, for example, as to have effectively segregated Chinese and Islamic traditions behind closed office doors for the better part of a millennium. Such was not always the case. In this paper, I will discuss how the culture of bureaucratic isolation emerged over the first millennium CE through public bans, institutional restructuring, and reforms in office education, testing and recruitment. What legendarily began as a hereditary office in pre-imperial times had become, by the second century BCE, a nexus of outside talent and public debate. From 104 BCE to 420 CE, for example, only 31 percent of office-holders named as contributing to state astronomical policy actually held a post in the Clerk’s Office, and those who did were usually the first in their family to do so; the history of the eighth-century office, by contrast, is one of family clans. For a time, the clans that ran this office were of foreign ancestry—the Indian Kāsyapa, Kumāra and Gautama, replaced by the Nestorian Li—but Indian and Persian technical knowledge ended up having little manifest influence on their Chinese colleagues’ practices. This paper will use the case of this first wave of foreign talent and transmission to examine how much the scientific and office culture of these centuries had changed since the Han, and how it adumbrated the conditions of later dynasties.