A port.
yes they can . a well trained and well fed team can pull loads three times their body weight or more on a flat bottom sled over dry ground .i do not know the record but i know that two oxen have...
Horses carry heavy loads. mainly Clydesdales.
Usually Horses can pull heavy loads....It depends on how heavy the load is really....It if was luggage, a horse could do the job!
Sometimes, in the old days, sheep would carry heavy loads.