I found an interesting, short paper doing a bit of forensic investigation on Charlemagne
Charlemagne (ca. 747814 CE; Fig. 1) or Carolus Magnus meaning Charles the Big as well as Charles the Great is one of the most important historical personalities. Being son of Pippin the Short (714768 CE), his physique is only known from historical descriptions, which may be biased by his political greatness reflected in his title of Pater Europae. His friend and courtier Einhard (ca. 770840 CE) described him as a large and strong person, being lofty but not disproportionally tall, and measuring exactly seven times the length of his own foot (Einhard, 1880). Charlemagne's earthly remains are inaccessible since he was canonised in 1165 CE and as sacrosanct his bones are sealed in the sarcophagus at the Aachen cathedral in Germany. However, the left tibia (Fig. 1) exhibited in the cathedral's treasury was made available for our study by Church authorities.
They found he would have stood around 184 cm, putting him in the 99th percentile for height in his day. That’s only around the 75th percentile for height now in the same area – a reminder of how much stature has increased in post-industrial Europe.