Duodecagonal

[…]the Luſitanian Cicero (as his countrymen call him) proceeds to tell his audience, that “if the Supreme Being was to ſhow himſelf under any geometrical figure, it would certainly be the circular in preference to the triangular, the ſquare, the pentagonal, the duodecagonal, or any other known to the geometricians.

[…]the town-house is splendid, it is built on a public square, adorned with a tower and clock, similar to that of Lyons, a high column with a brazen statue of the Blessed Virgin, entirely gilt, a large water reservoir of a duodecagonal figure, and with a statue on a pedestal in the centre;

One of the interesting spots on the place is known as Guy’s Tower, duodecagonal and almost a hundred feet high, pierced by forbidden mullioned windows and loopholes.

Every monastery and cathedral had a chapter house. They were nearly always rectangular and were the most important building after the church itself. Thirty centrally planned chapter houses were constructed between 1100 and 1500: although about two thirds were octagonal, there are circular, decagonal and even duodecagonal examples.