Round barns... their peak in popularity was from about 1880 until the 1930s. Earlier versions were actually octagonal, but in the 1880s true circular barns were built. Their design is based on the principal that a circular plan has a greater volume-to-surface ration than a box shape. Attractive and attention-getting, their scale and perspective can be are deceiving - I spotted the first barn from about 2.5 miles away, and thought several times that I must almost be there and that surely the barn is at the next farm. Three times I was fooled by the 60' giant.
Pic #1 - North-East of Arcanum, 60' true round, built 1910, moved here from Indiana in 2001. Beautiful condition, massive structure. No one home, so I only took one picture. Note the metal flag on top indicating wind direction, and the ball on top (lightening rod?).
Pic #2 - South-South-East of Gettysburg, 50' octagonal, year unknown. Good condition, attached to rectangular barn, both behind immaculate ranch-style home. No one home, so I took just this one quick photo.
Pic #3 - South of Gettysburg, 45' octagonal, built in 1910. Owner was home... got to speak with him awhile, and he let me roam around the barnyard taking pictures. Attached to a rectangular barn which has a recent new roof, but the round barn has an older roof which has suffered quite a bit of damage on the weather side (SSW). Owner can't afford to have roof replaced (at about $5000 to $7000), so it's gonna get worse before it gets better. Note scale of barn, especially in comparison to my bike parked next to it, and this was the smallest of the three!
(Barn info copied from Dale J. Travis' web page http://www.dalejtravis.com/rblist/rboh.htm )