The American Heritage® Dictionary of the English Language: Fourth Edition. 2000.
Appendix I
Indo-European Roots
ENTRY:
merg-
DEFINITION:
Boundary, border. Oldest form *mer-, becoming *merg- in centum languages. Derivatives include marquee, demarcation, and margin. 1a.mark1, from Old English mearc, boundary, landmark, sign, trace; b.margrave, from Middle Dutch marc, border; c.march2, marquee, marquis, marquise, from Old French marc,marche, border country; d.marchese, marchioness, from Medieval Latin marca, boundary, border; e.demarcation, from Old Italian marcare, to mark out; f.mark2, from Old English marc, a mark of weight or money; g.markka, from Swedish mark, a mark of money; h.marka, from Middle High German marke, mark of money. a–h all from Germanic *mark-, boundary, border territory; also to mark out a boundary by walking around it (ceremonially “beating the bounds”); also a landmark, boundary marker, and a mark in general (and in particular a mark on a metal currency bar, hence a unit of currency); these various meanings are widely represented in Germanic descendants and in Romance borrowings. 2.letters of marque, marquetry; remark, from Old Norse merki, a mark, from Germanic *markja-, mark, border. 3.marc, march1, from Frankish *markn, to mark out, from Germanic denominative verb *markn.4.margin; emarginate, from Latin marg, border, edge. 5. Celtic variant form *mrog-, territory, land. Cymry, from Welsh Cymro, Wales, from British Celtic *kom-brogos, fellow countryman (*kom-, collective prefix; see kom), from *brogos, district. (Pokorny mere- 738.)
-, becoming *merg- in centum languages. 
n, to mark out, from Germanic denominative verb *mark
