Today, it’s hard to find cast or wrought iron of any sort for structural purposes like fencing. The majority of what is produced is small or purely decorative ornamentation. In fact, the largest examples of iron you can easily find are large decorative wall panels. To create a pure cast iron fence, you would have to hire a skilled worker to weld pieces together into larger panels. This will be expensive, take a lot of time, and the final product would still likely depend on steel top and bottom rails as well as posts for its strength. Wrought iron stock for rails and balusters is meant for limited use—mainly restoration work—and getting ahold of enough stock for a large residential fence is difficult, and stunningly expensive. The end result of all this effort would be a fence that is notably less durable than one built of cheaper and more widely available steel.