Layer sugar, figs and lemon slices in large pot and cook covered on very low heat until sugar dissolves (about 1 hour). Uncover and cook about 45 minutes longer, until figs are transparent.
Lift out figs with a slotted spoon and cook the syrup about 15 minutes longer, until thicker. Put figs back into pot and let sit overnight.
The following morning, heat figs to a boil and seal in jars.