After the Battle of Buxar, 1764, the Mughals as well as the Nawabs of Bengal lost effective control over the territories then constituting the province of Bengal, which currently comprises the Indian states of West Bengal, Bihar, Jharkhand, Orissa, and Bangladesh. The British East India Company was accorded the diwani rights, that is, the right to administer the collection and management of revenues of the province of Bengal, and parts of Awadh, currently comprising a large part of Uttar Pradesh. The diwani rights were legally granted by Shah Alam, who was then the sovereign Mughal emperor of India. During the rule of the British East India Company in Bihar, Patna emerged as one of the most important commercial and trading centers of eastern India, preceded only by Kolkata.
Under the British Rule, Bihar particularly Patna gradually started to attain its lost glory and emerged as an important and strategic centre of learning and trade in India. From this point, Bihar remained a part the Bengal Presidency of the British Raj until 1912, when the province of Bihar and Orissa was carved out as a separate province. When the Bengal Presidency was partitioned in 1912 to carve out a separate province, Patna was made the capital of the new province of Bihâr and Orissa. The city limits were stretched westwards to accommodate the administrative base, and the township of Bankipore took shape along the Bailey Road (originally spelt as Bayley Road, after the first Lt. Governor, Charles Stuart Bayley). This area was called the New Capital Area.
The Patna Secretariat with its imposing clock tower and the Patna High Court are two imposing landmarks of this era of development. Credit for designing the massive and majestic buildings of colonial Patna goes to the architect, I. F. Munnings. By 1916-1917, most of the buildings were ready for occupation. These buildings reflect either Indo-Saracenic influence (like Patna Museum and the state Assembly), or overt Renaissance influence like the Raj Bhawan and the High Court. Some buildings, like the General Post Office (GPO) and the Old Secretariat bear pseudo-Renaissance influence. Some say, the experience gained in building the new capital area of Patna proved very useful in building the imperial capital of New Delhi.
The British built several educational institutions in Patna like Patna College, Patna Science College, Bihar College of Engineering, Prince of Wales Medical College and the Patna Veterinary College. With government patronage, the Biharis quickly seized the opportunity to make these centres flourish quickly and attain renown. In 1935, certain portions of Bihar were reorganised into the separate province of Orissa. After the creation of Orissa as a separate province in 1935, Patna continued as the capital of Bihar province under the British Rule.
Source : Wikipedia