What is "excubitors"

The Excubitors ( or excubiti, literally "those out of bed", i.e. "sentinels"; ) were founded in c. 460 as the imperial guards of the early Byzantine emperors. Their commanders soon acquired great influence and provided a series of emperors in the 6th century. The Excubitors fade from the record in the late 7th century, but in the mid-8th century, they were reformed into one of the elite tagmatic units, the professional core of the middle Byzantine army. The Excubitors are last attested in 1081.