The Changing of the Guards originated in the 15th century. The guards were in charge of opening and closing the gate, inspecting all visitors, and keeping watch. The ceremony now is a reenactment complete with traditional weapons, musical instruments, and colorful robes. The facial hair you see on the "soldiers" below isn't real, it's just part of their costume!
"A traveler without observation is a bird without wings."
~Moslih Eddin Saadi