In 1863 the English Football Association decreed that the posts should be 8 yards apart (7.32m), a measurement which has never altered since. Because players often argued whether the ball had gone between the posts (for a goal) or above (no goal), tape was then used to join the tops of the posts (1865).
In 1866 the English Football Association decreed that “The goals shall be upright posts, eight yards apart, with a tape across them, eight feet from the ground”. By 1875 the wooden crossbar started to replace the tape.
Round or square-shaped goals were the most common until, in 1920, a Mr. J. C. Perkins of the Standard Goals company in Nottingham, England, invented the much stronger elliptical shape. Nottingham Forest was the first club in the world to try them. Many Scottish clubs stayed with their square designs for many years, but elliptical posts and bars are now the favourite around the world. Though they too can still break.
Until the 1980s, most goals were made from wood. Douglas Fir was often the preferred choice of wood. In recent years, however, much lighter aluminium or steel goals have become more popular, especially with ground staff because maintenance is now a lot easier.
But the goal post has basically remained unchanged for well over a century.