Ancient and early medieval temples feature smaller "gopuram", while in later temples they are a prominent feature of Hindu temples of the Dravidian style; or in many cases the temple compound was expanded and new larger gopuram built along the new boundary. They are topped by the "kalasam", a bulbous stone finial. They function as gateways through the walls that surround the temple complex. Another towering structure located towards the center of the temple is the Vimanam. Both of them are designed and constructed as per rules given in the texts of Vaastu shastra.