Heron's formula for the area of a triangle

Given a triangle with sides $a, b$ and $c$ Heron's formula is:

$$A=\sqrt{p \cdot (p-a) \cdot (p-b) \cdot (p-c)} $$

where $p$ is the semiperimeter:

$$p= \dfrac{a+b+c}{2}$$

It works when all the sides of a triangle are known we can calculate the area with no need to know the height.