What defined the ownership of a treasure in Jesus' time?

Matthew 13:44 reads: > The kingdom of heaven is like treasure hidden in a field, which someone found and hid; then in his joy he goes and sells all that he has and buys that field. One is intrigued by the step-by-step action of the finder. He could have easily taken the treasure. That prospect leads one to believing that there was some law which defined the ownership of a treasure, both legal and moral. (These days it usually goes to the Government, whoever be the one who finds it, and whatever be the place it is found in!). Are there any studies into the legal system prevailing at the time of Jesus that defined the ownership of a treasure ?