Padlocks are portable locks

Lock (device)

A lock is a mechanical or electronic fastening device that is released by a physical object or secret information , or combination of more than one of these....

 used to protect against theft

Theft

In common usage, theft is the illegal taking of another person's property without that person's permission or consent. The word is also used as an informal shorthand term for some crimes against property, such as burglary, embezzlement, larceny, looting, robbery, shoplifting and fraud...

, vandalism

Vandalism

Vandalism is the behaviour attributed originally to the Vandals, by the Romans, in respect of culture: ruthless destruction or spoiling of anything beautiful or venerable...

, sabotage

Sabotage

Sabotage is a deliberate action aimed at weakening another entity through subversion, obstruction, disruption, or destruction. In a workplace setting, sabotage is the conscious withdrawal of efficiency generally directed at causing some change in workplace conditions. One who engages in sabotage is...

, unauthorized use, and harm. They are designed to protect against some degree of forced and surreptitious entry.
The first padlocks were "convenient" locks so they could be carried and used where necessary.

The earliest positive evidence of padlocks comes from the Roman Era, 500 BC–300 AD.

They were known in early times by merchants traveling the ancient trade routes to Asia and China.