There are somewhere around 230 strings in a piano. They range from a speaking length of only 2″ to 7 feet or more. In the low bass there is only one string per note. Then in the upper bass, 2 strings per note. In the middle and treble there are 3 strings per note. This is to balance out the loudness of each area. The upper strings are plain steel wire. Although they all look alike, there are many sizes of plain wire that are only .001 inch different. In the bass section, the strings have copper windings around them to make them heavier so they will vibrate more slowly. The lowest notes can have 2 layers of copper to make them large without making them too stiff.
Tuning a piano involves adjusting every string. I first get one of the strings in the right relation to notes around it, and then tune the unison to match the other two strings to the one already tuned.
Piano wire is probably the strongest material in your house. It is very difficult to make it hard and strong enough without it becoming brittle and breaking easily.