In ancient times people used which of the following to measure length? 

The metre is the common unit of measurement, however for convenience, other length units including centimetres, millimetres, and kilometres may also be used. The scale at which the length is to be measured determines the sort of units to be used.
Measurement is the practise of comparing an object to a standard unit of length measurement, known as the metre. Numerous things can be used as length measuring units.

Hand span, forearm length, or footstep can all be used as units of measurement for determining an object's length. However, due to individual differences in length, hand spread, forearm length, and footstep cannot be employed as a standard unit of measurement. Various persons have different hand-span, forearm, and footstep lengths. From one to person, it differs. Therefore, the lengths of the hand, forearm, and footstep are not measured in the same way.
However, in the past, length was measured using a hand span.

A standard unit of measurement of length is one that has a defined value and does not vary from person to person or location to location. A metre symbolises precisely the same length whether it is used by one individual or another, whether it is used in one nation or another. No matter who you are or where you are, the meter's length remains constant. For the sake of measuring consistency, standard units of measurement must exist.
In the past, neither a wooden scale nor a metre tape were utilised. It is a commonly used tool for measuring length.

Hence, the correct answer is option C.