The basic tools haven't changed all that much in the past few millennia. For vertical levels, plumb lines have been in use for essentially all of recorded history. A string, made from some local fiber, is woven around a weight and gravity pulls the line straight. For horizontal levels, there are several different types. Various types of spirit levels have been created at different points. For instance, we know some of the Puebloans used a water variant of the spirit level for construction. It's also possible to simply use a straightedge or a ruler for certain types of work. The greeks famously had such devices and many rocks have planar cleavage faces that are suitable. We still use versions of all of these tools today, alongside their more modern counterparts.