… originally, duties of the common carriers were simply those of bailees in general, coupled with the liabilities attached to the exercise of a public calling and were not peculiar to common carriers only but were regarded as the custom of law of common hoymen, or lightermen, etc., according to the business of the party concerned.
Coggs v Bernard (1703) 2 Ld.Raym 909 per Holt CJ:
…I must show the several sorts of bailments. And there are six sort of bailments. The first sort of bailment is, a bare, naked bailment of goods, delivered by one man to another to keep for the use of the bailor; and this I call a depositum, and it is that sort of bailment which is mentioned in Southcote’s case. The second sort is, when goods or chattels that are useful are lent to a friend gratis, to be used by him; that is called commodatum because the thing is to be restored in specie. The third sort is, when goods are left with the bailee to be used by him for hire; this is called locatio el conductio, and the lender is called locator, and the borrower conductor. The fourth sort is, when goods or chattels are delivered to another as a pawn, to be a security to him for money borrowed of him by the bailor; and this is called in Latin, vadium, and in English, a pawn or a pledge. The fifth sort is when goods or chattels are delivered to be carried, or something is to be done about them for a reward to be paid by the person who delivers them to the bailee, who is to do the thing about them. The sixth sort is, when there is a delivery of goods or chattels to somebody who is to carry them, or to do something about them gratis, without any reward for such his work or carriage, which is this present case. I mention these things, not so much that they are all of them so necessary in order to maintain the proposition which is to be proved, as to clear the reason of the obligation which is upon persons in cases of trust.