In Aussy  - in the area I live - there is gravel in the hills about 30 miles from our flat grain growing country. And a town, also in the hills, originally started on gold mining, followed by grazing of livestock -  mainly sheep.
There were two firms in the town who made and sold concrete posts. The ones used for normal line posts were 'half round' on one side, flat on the other, [as some other poster described] , and had holes to thread plain wire through, or alternately to tie fabricated fencing to.
I have some that have been in the ground more than 60 years and are still in good condition, but there are others that have had the moisture penetrate the concrete and rust the re-enforcing rod, shattering the post.

It's a long time ago, but I seem to remember when one firm went out of business, the story got around was that the employees were reducing the amount of cement in the mix, and stealing the surplus to do their own concreting jobs at weekends.  Pathways, shed floors or similar. This - of course - resulted in sub standard posts!

Normal 'line' posts weighed 112 lbs. [1 cwt - or 20 to the ton.] 
Line 'strainers' were square, and 2 cwt in weight.  - 224 lbs.
"Corner" strainers were 4 cwt  - or  'bl***y heavy'!  About 10 inches square and 7 ft long.
The firms also made stays and blocks for where a gateway was to be in a fence line, or where there was an intersection in the roads, and a ninety degree corner created..

When both firms were no longer operating, I went to driven pine posts for my fences. Wire - either plain or manufactured  - stapled to the pine posts. The fences I built replaced original fences that were 60 to 80 yrs old!