Below the salt
Common or lowly. See also 'beyond the pale'.
'Below the salt', or 'beneath the salt', is one of the many English phrases that refer to salt, for example, 'worth one's salt', 'take with a grain of salt', 'the salt of the earth', etc. This is an indication of the long-standing importance given to salt in society.
One of the few explanations that begin "In mediaeval England people used to..." that is actually correct.
In mediaeval England salt was expensive and only affordable by the higher ranks of society. Its value rested on its scarcity. Salt was extracted from seawater by evaporation and was less easily obtainable in northern Europe than in countries with warmer climates, where the evaporation could be brought about by the action of the sun rather than by boiling over a fire. This method was abandoned in England in the mid-1600s when natural rock-salt began to be mined commercially in Cheshire. Prior to that date the high value of salt was the source of the high symbolic status given to it in the day-to-day language that originated from England in the Middle Ages.
At that time the nobility sat at the 'high table' and their commoner servants at lower trestle tables. Salt was placed in the centre of the high table and only those of rank had access to it. Those less favoured on the lower tables were below (or beneath) the salt.
The term 'salt' is used for the container the salt was kept in as well as for the condiment itself. The ornate design and costly materials used for these salts was a reflection of the importance that salt was accorded. As early as 1434 the word 'salt' was used in this way, e.g. "A feir salt saler of peautre." (A fine-quality pewter salt cellar). Strictly speaking, to be 'below the salt' was to be below the salt cellar.
The phrase was in figurative use by the late 16th century, as this quotation from Ben Jonson's Cynthia's Revels, 1599 shows:
"His fashion is not to take knowledg of him that is beneath him in Cloaths. He never drinks below the salt."