In Hindu tradition, temples are considered as the abode and bodies of gods. Though the earliest Hindu shrines and temples were small and simple structures, with the passage of time temples grew more varied and complex in plan and elevation, gradually including a variety of subsidiary structures within their compounds. The exterior walls of the temples are richly overlaid with carvings and sculptures, a teeming assembly of male and female figures, animal, vegetable and floral forms, mythic images of gods and goddesses, divine and semi-divine beings - all representing the entire panorama of the life of nature. In contrast, the innermost cella, the womb-chamber (Carbhagriha), lies hidden among the folds of the massive outer walls, reached through a series of ceremonial halls and stairways, whose walls and ceilings are covered with paintings or lined with icons installed in niches. These halls lead gradually up from ground-level, the mundane, to the highest regions of the spiritual, opening finally on to the dark, relatively small Garbhagriha, where an image or emblem of the temple's tutelar deity resides. The Garbhagriha represents the culmination of the individual's search and is the sanctum sanctorum of the temple. It lies directly beneath the temple's spire.
Whether humble sanctuaries or complex temple compounds, all Hindu temples have been built on the scheme of the ritual diagrams, yantras and mandalas. These yantras are of a specific type, different from those used for personal ritual worship and meditation.
Architectural yantras are not ground-plans for temples but schematize the principles on which the sacred precincts of the temples are constructed. The dimensions and measurements of temple architecture are specified in early architectural manuals that also prescribe rituals to accompany the laying-down of a building's basic plan.

The Vastu-Purusha Mandala
Most manuals stipulate that the ground-plan of every Hindu temple must conform to a simple graph, similar to a yantra, called the Vastu-Purusha Mandala, which was also the model for early towns. This diagram is basically an imprint of the ordered cosmos and reveals the form assumed by the Universal Purusha as a mandala in the phenomenal world (Vastu = bodily existence or site; Purusha = Supreme Principle or source of the cosmos: mandala = closed polygonal figure). The precise proportions of the Vastu-Purusha Mandala are not of importance since jt is never an exact blueprint of the ternp1e but a 'prognostication' or 'forecast' within which a wide range of possibilities of temple architecture is implied. The ritual diagram is an 'ideogram', while the temple is a materialization of the concepts it embodies.
The Vastu-Purusha Mandala is basically a square of squares but it can be converted into other primal shapes. The simplest arrangement consists of 64 (8 x 8) or 81 (9 x 9) squares, in which the nuclear central zone of 4 or 9 divisions is dedicated to the principal deity, Brahma. Other, more highly complex, types can be elaborated by gnomic progression into 1,024 squares. When the mandala is used architecturally its central zone locates the temple's womb-chamber. Around the nucleus, 12 squares are designated as seats of divinities, with specific reference to the 8 directions of space. These are surrounded by another .12 divinities associated with celestial bodies (28 lunar and 4 that preside over solsticial and equinoctial points).
Thus this simple graph-like diagram not only represents the energies of the directions of the compass but has astronomical connotations, providing a chart of cyclical revolution, of day, month, year, etc. These mandalas, of which Hindu manuals of architecture provide thirty-two variations, are the earliest type of architectural yantras, contributing substantially to the rhythms, designs and conceptual basis of the Hindu temple.
South Indian architectural yantras are generally constructed to reflect a different cosmic order. Three concentric squares create a hierarchy: the innermost is assigned to the Universal Being, the middle square is the sphere of gods, the outer square the terrestial region. Beyond the outer square are the creatures of the netherworlds. The Sthandila Mandala of South India, however, resembles North Indian architectural yantras, being generally a composition of 49 squares.
Though architectural yantras are highly symbolic mathematical constructs they nevertheless provide certain practical indications. The Vastu-Purusha Mandala sets out the position of the devata images in a temple, while its use in planning a town prescribes the town's orientation and the sites where temples are to be constructed. Before a temple is built, the ground is levelled, purified and consecrated, and the Vastu-Purusha Mandala is ritually drawn on the site. Thus 'the building draws its power from the Vastu-Purusha [Supreme Principle] who lives at its base and converts, by his presence, the plan of existence [Vastu Mandalal into the shape of the Purusha, in whose likeness the temple is set up',
 

Sakti and Yogini Yantras

Tantrism puts great emphasis on the use of yantras in temple architecture, especially for the construction of temples devoted to sakti worship. Not only was the architectural yantra used as the basic inspiration for the plan and elevation of the temple, but yantras were actually incorporated into the fabric of the building. Yantras were, for example, laid into the foundation of the Carbhagriha and into important angles of the temples. Yantras also influenced the composition of the numerous sculptural images adorning the outer and inner temple walls (see below). A recently discovered tantric manuscript from Orissa (Silpa-Prakasa, 9th-12th centuries) has thrown light on the distinctive features of the specifically left-hand' tantric Sakti temples and their architectural planning rituals. According to this manual, at the appropriate site a peg is placed in the ground, symbolizing the central axis of the universe and called the womb of the yantra' (yantra-garbha). A circle is drawn around the peg and ten cardinal points are marked off relating to the regions of space (the eight directions, the nadir and zenith), to each of which is assigned a specific divinity. These ten points determine the entire plan of the temple. The construction from the centre outwards parallels the construction of yantras for worship and meditation,4 and the peg is analogous to the bindu.
The principal architectural yantra of Devi(Goddess) temples, as prescribed by the Sitpa-Prakasa, is rectangular, as opposed to the square of the Vastu-Purusha Mandala. Whereas the square is a static form, with four fixed points, the rectangle of the Devi temples symbolizes the rhythmic continuity of the creative play of Sakti, and her invincible power over life and nature. The Yogini Yantra, which is meant to be installed in Sakti temples, does not dictate the plan of the temple but reinforces the pre-eminence of Devi's power in a ritual during the construction of the temple. The Yogini Yantra is drawn on the base of the womb-chamber, and then consecrated and worshipped by the priest. After these preliminary rites, it is covered over and laid into the foundations of the innermost sanctuary. The symbolic meaning of the Yogini Yantra is as complex as that of the Vastu-Purusha Mandala, incorporating various elements of the tantric conception of the cosmos. Three points on the median line running north to south denote the threefold manifestations of Sakti exhibited through her threefold tendencies: sattva, rajas, tamas (purity or intelligence, energy, mass or inertia]. Three rajas-triangles indicate dynamic activity behind creation, balancing the opposing forces: the ascending tendency, the two sattva-triangles at the top, the descending tendency, the two tamas-triangles at the bottom. The seven triangles stand for the attributes of the DevT, who is the primary source of all creation.
In the outer points of each triangle, a cluster of 64 goddesses, known as the sixty-four yoginTs, are invoked. These divinities represent the rhythmic cycle of day and night which is divided into 30 parts (muhurtas) - 15 for day and 15 for night. Each muhurta is presided over by two of these yoginis, with two yoginis each for dawn and twilight. The Yogini Yantra is installed in the Varahi Temple (c. 12th century) in Caurasi, Orissa, where esoteric practices such as sexo-yogic rites, virgin worship, etc., were practised by the 'left-hand' tantrikas (Kulacharas).
The use of yantras in tantric shrines dedicated to Sakti extends beyond prescription for the plan and preliminary rites. The esoteric aspect of the left-hand doctrine is vividly illustrated in the imagery of the Kamakala Yantra. This yantra, considered exceedingly potent, is either a square or rectangle, and has the Siva emblem of the liriga rising from the centre of the base line, around which there are sixteen yoni triangles, each presided over by a Sakti. Above the linga is a dot which is the abode of the Supreme Sakti, Maha- Kama kales van. This yantra is considered necessary for every temple devoted to Sakti and Siva, warding off any obstacle that may hinder the sadhana of the worshippers in the temple. In addition, the Kamakala Yantra has an esoteric meaning, and was always to be concealed under the mithuna (amorous couple) images installed in the temple. This yantra expressed the quintessential philosophy of the left-hand practitioners, who believe that ‘Desire is the root of the universe. From desire all beings are born. Primordial matter (Mulabhuta) and all beings are reabsorbed again through desire, so the text concludes that a place without love-images (kamakala) is.a.p|ace to be shunned’ It has been mentioned above that in tantric temples yantras were applied to regulate the design and creation of the sculptures adorning temple walls.11 Such 'compositional yantras' are not used for meditation or worship but to provide an abstract framework, based on mathematical proportions, which determines certain fundamental compositional principles for the execution of sculptures of devatas such as the ten Mahavidyas, and especially for the presiding deities of tantric shrines. The basic schemes of the compositional yantras may be a grid of vertical, horizontal and oblique lines, with a central focus. It is on the basis of the line divisions of these yantras that the whole sculptural image is built up. Each type of yantra matches an image of a particular deity. We may infer the immense role yantras have played in tantric temple art.

The Surya Pancabja Mandala and Navagraha Yantra
A particularly fine example of a temple based on and incorporating yantras is the magnificent Surya Temple in Konarak near Bhuvanesvar in Orissa. This was built about AD 1240-80 in honour of Surya, the Sun God, source of all light, spiritual and earthly. Recent research7 has shown that yantras were embedded in the pedestal of the presiding Surya image. The temple had two principal structures; a high tower (Vimana), now in ruins, in which the cult image of Surya was placed, and a step-pyramidal assembly hall Oagamohana) that led into the inner chamber of the sanctuary. The manner of construction of the yantra underlying the shrine, the Surya Pancabja ( = 5 lotuses) Mandala, and of worshipping its various devatas, is explained in a tantric manual :
This Saurapancabja Mandala is greatly loved by Surya; it is made for the worship of Surya together with four other devatas. For this yantra a square has to be made with divisions and subdivisions, so that the whole field is divided into twenty-five parts.
By tracing two diagonals the centre-point is found. Around the centre, a circle with eight sectors has to be drawn not exceeding the size of the central division.
The lotus in the centre is eight-petalled; in the corners are twelve-petal led lotuses. ...
In the centre of this yantra is a bindu, and a hexagram inside the circle with an eight-petal led lotus.
On the south side Ganesa and Rudra, on the north side Ambika and Vishnu, are to be worshipped [on the small lotuses]. Then, leaving a half-part of i\the outer square, a square is made with a karnika [ear] in each of the corners. In those karnikas three bindus are to be made. Two are on the sides and one in the centre. On these three bindus the Surya Saktis are worshipped.
In the Agni [south-east] corner Dipta, Suksma and |aya; in the Nairrtya [south-west]' corner Vijaja, Bhadra and Usma. In the Vayu Inorth-west] corner Tiksna, Vega and Pracanda; in the Isana [north-east] corner Tapini, Svarnamsu and Akskarika.
These have to be worshipped with seed mantra Hrim, with flowers, perfume and rice they have to be worshipped.
Again, in the second half of the square, the corners are to be left as they are, and one section by their side.
The Dikpalas [deities of the regents of space] have to be worshipped. On all four sides the bhupura [outermost periphery] has projecting parts like portals. The Dikpalas are worshipped with their mantras in their proper places. Only by the side of the front Brahma and Ananta have also to be worshipped.
Surya puja is done in the centre with [Surya's Saktis] Chaya and Maya.
The Smartas [Brahmins] worship the five Devatas on this place.
Hrirn bija [seed sound] is for Surya, Klirn bija for Vishnu, Gum for Ganesa, Sri bija is for Ambika. Rudra is worshipped with the Rudra-mantra by the Smartas.
When a hall is built for a sacrifice [yajna] to Surya it is to be built according to this yantra, including all the four circles, with an altar [vedika] in the centre.
The central axis of the temple as it was built coincides exactly with the centre of the yantra laid into its foundations, and an imaginary line drawn vertically upwards from the centre of the yantra would strike the apex of the monument. Similarly, the four small lotuses in the four corners of the mandala correspond to the four pillars that still support the roof of the temple.
Adjacent to the main temple, a structure used as a ceremonial hall (Nat-Mandir) is based on the Yantra of the Nine Planets (Navagraha Yantra). As Surya is the Lord of Planets, his worship is always accompanied by the worship of celestial bodies and their revolutions. The yantra is a square grid of nine units, each compartment presided over by a planetary divinity, with Surya's place at the centre of the yantra.. The Nat-Mandir is an architectural replica of the yantra, with the raised podium of its ceremonial hall divided into nine equal square compartments. The nine divisions are created by sixteen massive pillars, each of which stands at the corner of one or more squares. The Nat-Mandir was used for daily rites during which a portable image of Surya was placed in the centre of the platform, corresponding to the place assigned to Surya in the yantra, and worshipped at dawn when the rays of the rising sun fell upon it.

Stone mandala
The relationship of yantra and architecture is especially close in monuments which may be called 'mandalas in stone'. A striking example is the Buddhist Barabadur Stupa (8th century AD) in Indonesia, which rises like a terraced mountain with nine levels corresponding to the nine circuits of the Sri Yantra. Built on a square foundation, with four doorways and five walled-in terraces, it has three circular structures with innumerable images of the Buddha. Finally, the ninth level is crowned with a terminal stupa which is the realm of the Supreme Buddha.
The Sri Yantra itself is essentially three-dimensional, like a terraced mountain, and both yantra and stupa represent the cosmological scheme of the mythical 'world-mountain', Mount Meru. As Paul Mus9 has demonstrated in his study of Barabadur, the internal design of the temple can best be understood through a description of the Sri Yantra.
The Barabadur Stupa like the yantra is conceived as a place of spiritual pilgrimage. In the stupa the journey starts at one of the four doorways, and continues through the lowest galleries, which illustrate in relief scenes from the Buddha legends representing the world of desire and illusion. As the pilgrim moves in a spiral to the upper terraces which open out to the sky, the Buddha images become more and more abstract — a change which represents the transition from the world of matter to the world of the spirit. It parallels the sadhaka's journey from the material to the spiritual during meditation on the Sri Yantra. Movement from the lower, outermost levels to the centre, the summit/bindu, is to be translated from the world of matter to the world beyond thought.