St. Mary's Hall, and designed to be in keeping with its medieval surroundings, began in 1913 but was delayed during World War I. It was completed by 1917, but was not officially opened until 11 June 1920 by the Duke of York – later to become King George VI. As late as the 1920s, Coventry was being described as "The best preserved Medieval City in England". On visiting the city (before the devastation that resulted from the Blitz), the novelist J. B. Priestley wrote: "I knew it was an old place, but I was surprised to find how much of the past, in soaring stone and carved wood, still remained in the city." However, the narrow medieval streets proved ill-suited to modern motor traffic, and during the 1930s many old streets were cleared to make way for wider roads, creating an odd mix of medieval and contemporary streets and buildings. The city remained prosperous and largely immune to the economic slump of that decade. During the 1930s the population of Coventry grew by 90,000. There had been yet another boundary extension in 1928 which brought even more districts within the city limits, and extensive new housing estates were rapidly developed, particularly within those districts, though barely fast enough to keep pace with demand. By 1947 Coventry's boundaries enclosed 19,167 acres (77.57 km2). Catering to the needs of the city's growing population, the Coventry Corporation Act 1927 reassigned Whitley Common, Hearsall Common, Barras Heath, and Radford Common as recreation grounds, and ended all the remaining traditional commoning rights on waste ground in Coventry, and the freemen of the city, who had been allowed to have up to three animals grazing on these areas since 1833, each received an annual sum of £100 as compensation. The council had already purchased Styvechale Common from the Lords of Styvechale Manor following the First World War to create the War Memorial Park, and in 1927 a monument was built in the park to commemorate all Coventrians that died in that war, and since then later conflicts also. Starting in 1931, large sections of the city centre were demolished to make way for a new street plan, more suited to the motor car, with the timber-framed buildings to be replaced by modern structures. Initially, Fleet Street was replaced by Corporation Street, and in 1937 Little Butcher Row and Great Butcher Row gave way to Trinity Street.