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The fifth postulate is unnecessary
Euclides based his geometry on five postulates:
1. To draw a straight line from any point to another.
2. To produce a finite straight line continuously to a straight line.
3. To describe a circle with any center and distance.
4. That all right angles are equal to each other.
5. That if a straight line falling on two straight lines makes interior angles on the same side less than two right angles, if produced infinitely, meet on that side on which are angles less than two right angles.
The fifth postulate is superfluous. It follows directly from applications of the first four postulates for the following construction.
We take a square ABCD. All its right angles are according to the 4. postulate right, and all its four sides are straight lines.
We add to this square ABCD a new square CDEF and align the sides AE and BF according to the 2. postulate.
To the obtained rectangle ABEF, we and a new square EFGH and align again the sides AG and BH according to the 2. postulate.
In such a way we continue with adding of squares infinitely, eventually on the other shorter side of the rectangle.
In such a way we produce a pair of parallel straight lines connected by orthogonal columns of equal length.
There are two possibilities that the long sides of the infinite rectangle meet or diverge. Either these long sides are not straight lines meeting the demands of the 2. postulate, or the right angles of consecutive squares did not meet the demands of the 4. postulate.
The fifth postulate is a consequence of the application of two postulates from the first four ones for an infinite construction.