Text of Jesus Washing the Disciples' Feet at the Last Supper Video
Archeologists have found sandals dating back to the time of Jesus. Sandals (feet) are the dirtiest part of the body, so at a formal meal you're supposed to have a foot washing with a basin and a towel. The Last Supper is remembered as a meal where Jesus volunteers to wash the feet cause none of the disciples did.
People back then would have realized that the lowest part of a reclining table is over here and that person should have volunteered to do it, but Jesus as a sign of humility offered to wash his disciples' feet.