Approximately 13 billion years ago, the radiation produced by the first galaxies completely transformed the Universe. The vast amount of hydrogen filling the space between galaxies was ionized in a process called cosmic reionization. Despite their intimate connection, the formation of the first galaxies and the reionization process are typically studied separately. An international team led by and including MPA researchers has now produced the first suite of simulations designed to simultaneously investigate these two processes during the infancy of the Universe, unveiling features of their connection. This new numerical effort – soon to be released publicly – provides a unique platform for investigating the young Universe and to fully exploit the forthcoming James Webb Space Telescope. The first results from THESAN have already shown that its unique combination of physical accuracy and simulated scales allows to reproduce most of the available data, including some that escaped previous numerical efforts.