Prayagraj, historically known as Prayāga and later Allahabad, is a significant city in the Indian state of Uttar Pradesh. Its ancient name, Prayāga, meaning 'place of sacrifice,' originates from Hindu beliefs that Lord Brahma performed the first sacrifice here. The city is globally recognized for the Triveni Sangam, the sacred confluence of the Ganges, Yamuna, and the mythical Sarasvati rivers, making it a pivotal pilgrimage site in Hindu scriptures, including the Rigveda and Mahabharata [1]. Prayagraj also holds importance in Jainism, with Purimtal being a revered site where the first Tirthankara, Rishabhadeva, achieved kevalya gyana [1].

The city's historical narrative is further enriched by its association with the Mughal Empire; Emperor Akbar founded the city of 'Ilahabas' (later Allahabad) in 1584, strategically positioning a fort at the confluence. During the British Raj, Allahabad became a key administrative and political center, serving as the capital of the North-Western Provinces and later the United Provinces [1]. It played a crucial role in the Indian independence movement, with prominent leaders like Jawaharlal Nehru having strong ties to the city. In October 2018, the city officially reverted to its ancient name, Prayagraj, reflecting its deep cultural and spiritual roots [1].

• Prayagraj is the seventh most populous city in Uttar Pradesh and the thirty-sixth most populous in India, with an estimated population of 1.53 million in 2011 [11].
• As of January 2020, the Prayagraj Municipal Corporation expanded its boundaries to 365 km², with a population of 1,536,218 within these limits according to the 2011 census, resulting in a density of 4,200/km² [4].
• The city's literacy rate is 86.50%, with male literacy at 90.21% and female literacy at 82.17% [147, 148].
• Hinduism is the majority religion in Prayagraj city, with 76.03% of the population, followed by Islam at 21.94% [145].
• Prayagraj has a humid subtropical climate (Cwa), characterized by hot, dry summers, cool, dry winters, and a hot, humid monsoon season from June to August [122, 123].
• The city is situated in the southern part of Uttar Pradesh, within the Ganga-Yamuna Doab, a region primarily composed of alluvial soil and water [114, 121].

Prayagraj's administration is structured across various governmental layers, overseen by the divisional commissioner of Prayagraj, a senior Indian Administrative Service (IAS) officer. This commissioner is responsible for local government institutions, infrastructure development, and maintaining law and order within the division [151]. The district administration, headed by the district magistrate and collector (DM), an IAS officer, manages property records, revenue collection, and elections, and ensures public order [151, 159]. The DM is supported by additional district magistrates and a chief development officer, with the district divided into eight tehsils, each led by a sub-divisional magistrate [157].

Civic infrastructure and urban development are managed by the Prayagraj Development Authority (PDA) and the Prayagraj Municipal Corporation (formerly the Municipal Board of Allahabad, established in 1864, and becoming a Municipal Corporation in 1959) [163, 165, 167]. The city is divided into 80 wards, each electing a corporator to the municipal committee. The municipal commissioner, an Uttar Pradesh government-appointed Provincial Civil Service officer, is responsible for the corporation's executive and administrative functions [169]. Prayagraj also hosts the Allahabad High Court, the highest judicial body in Uttar Pradesh, and is notable for its historical connections to seven Indian prime ministers, earning it the moniker 'Prime Minister Capital of India' [2].

Prayagraj possesses a stable and diverse economy, underpinned by various sectors including state and central government offices, educational and research institutions, real estate, retail, banking, tourism, hospitality, agriculture-based industries, railways, transport, logistics, and manufacturing [177]. The average household income in the city is approximately US$2,299 [177]. A significant portion of Prayagraj's economy is driven by the construction sector [178]. The city is also home to over 10,000 unregistered small-scale industries, contributing to its secondary manufacturing and service sectors [180].

Industrial development is concentrated in areas like Naini and Phulpur, hosting various public and private sector companies such as Reliance Industries, ITI Limited, BPCL, and IFFCO [184, 186]. Notably, Bharat Petroleum Corporation Limited is developing a large refinery in Lohgara. The district's primary economic sectors also include tourism, fishing, and agriculture, with Prayagraj serving as a hub for India's agricultural industry [189]. Key agricultural crops include paddy, wheat, and various pulses and oilseeds, with linseed dominating oilseed production [191]. An integrated industrial township spanning 1,200 acres has been proposed by the Dedicated Freight Corridor Corporation of India to further boost industrial growth [182].

Prayagraj boasts a comprehensive infrastructure network supporting its diverse urban and economic needs. Its transportation system includes Prayagraj Airport (IXD), connecting the city to eleven major Indian cities, and Prayagraj Junction, a significant railway hub for the North Central Railway Zone, offering extensive connectivity across India [193, 196]. The city is well-served by a network of National Highways, including NH 19, NH 30, NH 35, and NH 330, facilitating road travel [202]. Notable bridges like the New Yamuna Bridge and Old Naini Bridge connect different parts of the city and its suburbs, while National Waterway 1 further enhances connectivity [203, 204, 207].

In terms of civic amenities, the Prayagraj Municipal Corporation manages solid waste, with the city generating approximately 5,34,760 kg of domestic solid waste daily [25, 208]. The city was a pioneer in Uttar Pradesh for implementing pre-paid electricity meters and is monitored by over 40 CCTVs at key locations [209, 211]. Healthcare services are overseen by the Department of Health and Family Welfare, Government of Uttar Pradesh, providing twenty-four administrative hospitals, including Motilal Nehru Medical College and its affiliated hospitals, alongside numerous private and specialized medical facilities [212, 213]. Urban planning initiatives, such as the development of a 1.35 km riverfront along the Yamuna and the restoration of historical buildings like the Allahabad Government Public Library, contribute to the city's ongoing infrastructure improvements [230, 231].