Vision is dynamic. After their onset, visual stimuli undergo a complex cascade of processes before awareness is reached. Even after more than a century of research, the timing of these processes is still largely unknown. In particular, how the brain determines what visual features belong together and therefore have to be integrated remains an enigma. Previously, it was found that the processing of stimuli significantly outlasts its actual presentation. Such stimulus persistence is the basis for feature integration over time. Here, I show that – contrary to what is often assumed – simple visual features are integrated over a surprisingly long period of time before awareness is reached. Further, I show that this integration is mandatory and human observers have no access to the original simple visual features.