Sorry Loni, but Will Whitfoot actually was Mayor of the Shire and lived in the Westfarthing, rather than Hobbiton; his office was in Michel Delving. At the beginning of the story he was Mayor, was deposed by Lotho who named himself Chief Shirriff.

Loni was right that after the scouring of the Shire in November S.R. 1419 (TA 3019), Frodo did serve as Acting Mayor (actually as Will's Deputy) until Will Whitfoot recovered from being the first of many who had been imprisoned in the Lockholes by Lotho and his Men. Frodo resigned and Will resumed the office on Mid Year's Day S.R. 1420 (TA 3020). In S.R. 1427 Will Whitfoot resigned and Samwise was elected Mayor of the Shire for the first of seven times. He resigned the office in S.R. 1476.

All this can be found in Appendix B to LotR as well as RotK, Book VI, Chapters 8 and 9.

Anyway, Vee had the right answer and gets the pretty bauble.

Who built Durthang and why

Torondor built the citatel to prevent and moniter the rebirth of mordor, like Cirith Ungol.