As an adjunct to the scriptures in establishing Ekantik Dharma and consolidating the framework of the Satsang, Bhagwan Swaminarayan constructed magnificent stone mandirs - buttressing Upasana - worshipping God in all His greatness and glory, and bhakti - unalloyed devotion. Towards the end of His second decade of work, He placed a greater emphasis on bhakti over detachment - vairagya, to foster love for God. This emphasis on bhakti culminated in the building of mandirs.¹
The mandirs served four major purposes:

1. as a permanent place for offering worship,
2. as a centre for religious gatherings and instruction,
3. as a centre for studying Sanskrit, devotional music and Vedic literature,
4. as centres of social services where alms, medicines, and clothes, were available to the poor and needy.
   

The origin of the first mandir, built in Amdavad is worth considering. In 1817 the Peshwa rulers handed over the city to the British. A.K. Heron, an officer in the Company sent for Swaminarayan's disciples in the city. He requested them to invite Bhagwan Swaminarayan to the city from Gadhada.² He had met Him earlier in Kheda, just after the yagna in Dabhan. In divine form, Maharaj had also saved him from a tiger, not far from the Amdavad's walls, near the river Sabarmati. He related this miraculous experience to the Collector, John A. Dunlop. Heron also praised the peaceable nature and calming influence of Swaminarayan's devotees. This pleased Dunlop since he wished to establish law and order in the city. He was having a tough time dealing with Koli looters entering the city at night through holes in the city's walls.³ After meeting Maharaj, land was granted in the city to build a mandir.
In an astonishingly short span of six years, from 1822 till 1828, Bhagwan Swaminarayan constructed six mandirs of exquisite beauty and architectural grandeur in Gujarat - Ahmedabad, Bhuj, Vadtal, Dholera, Junagadh and Gadhada. He delegated this monumental task primarily to the versatile Brahmanand. Under the Lord's inspiration and his genius, he procured land, finance, stone, labour, relieved tax duties, in addition to designing the mandirs! Anandanand and Nishkulanand also helped him^.4
The sadhus and devotees provided the labour, considered as seva - devotional service. The Lord Himself spiritedly carried stones on His head, hauling them up the hill from the river Ghela, to Dada's court, during the foundation laying of the Gadhada mandir. He also carried thirty-seven bricks in the Vadtal mandir's construction.⁵ These can be observed 'in situ' even today.
In keeping with Vedic tradition, the Bhakta-Bhagwan relationship Bhagwan Swaminarayan consecrated in these mandirs the murtis of Radha-Krishna, Nar-Narayan and Laxmi-Narayan. He reinforced the dual worship of Bhakta-Bhagwan - God along with His ideal Devotee. His own murti, named Harikrishna Maharaj, He consecrated in Vadtal.⁶ Interestingly, in the history of world religions, this is perhaps the first instance of monuments of worship being constructed in the life period of a religious founder.
He entrusted the day to day performance of the worship rituals in these mandirs to the sadhus.
At a time when the land was steeped in penury, finances scant, the construction of such grand temples attested to His innate divinity. Parekh summarizes: 'The very magnitude of the Temples is a striking and novel feature in the Province in which this movement has worked, and that it should have succeeded in having so many temples of such size and beauty in so short a time reflects no small credit on the power and influence of the Master. These are standing monuments to his spiritual genius, his great power of organisation, and remarkable co-operation among his followers.'⁷

Source References

1 Vachanamritam, op.cit., Gadhada II-27.
2 Dave, op.cit., Vol. IV., Invitation pp. 18-21, Heron's request to build mandir in the city, pp. 31-34.
3 Behram, Boman, B.K. The Rise of Municipal Government in the City of Ahmedabad.
Bombay: D.G. Taraporevala Sons & Co. 1937, state of city's walls, pp. 7-9.
4 Mashruwala, op.cit., p.53.
5 Dave, op.cit., Vol. V., p.259.
6 ibid., p.18.
7 Parekh, op.cit., p.113.