Dear Florent;

"It is the a.t.thakathaa to verses 155 and 156 of the Dhammapada and is
part of the Jaraavaggo."

Thanks. I found the following explanation of "setthi" :

"This term setthi is rendered as foreman of a guild, cityman, banker,
wealthy merchant, in the PTS dictionary. Whatever the English term we
hit upon, the references make it clear that this was a titular rank
bestowed on certain wealthy citizens as a mark of social eminence and
recognition by a king. The Jataka stories show that when a king came
across a very rich man he honoured him with the conferment of this
title. The stories also indicate that these setthis did a certain amount of
work for the king. The investiture was no doubt carried out
ceremonially, as was the custom in India. It is difficult to say whether all
these titular lords had any hand in the administrative affairs of the land;
but all setthis seem to have been represented by one chief setthi, who
seems to have had a place in the Council of State. (Ariyapala, M.B.
(1968) Society in Medieval Ceylon, Colombo, Ceylon, 104)

The term carries a lot of history along with it. Scanned some pages
explaining it:

http://jonfernquest.googlepages.com/setthi.pdf

With metta,
Jon