Yantra, Tantra, Mantra and Yoga are four pathways that lead a spiritual aspirant to reach his goal.
These days, the definitions of above paths are changed. For example these days we consider yantras are array of geometrical shapes on two-dimensional medium. But this is not whole picture of yantra. In Yantras, soushtava yantras, called as symmetrical yantras. They are more efficient than two-dimensional yantras, often called as raekheeya yantras. The great saints such as Kasyapa enuemrated these silpas as three dimensional soushtava yantras to implant godly energies on to the Earth.
In primal Indian culture the rishis with their great and vast knowledge selected some points to be treated with godly energies from higher domains to establish balance and harmony on earth. So they constructed temples and great structures according to Silpa sastra and Vaastu. But during the course of time lots of such great constructions were damaged. Very few of them remained as icons of that glorious past.