The detailed regulations of the Japanese court state, in fifty books, supplementing the ritsuryō codes. Its books on the offices of the Left and Right Capital record the plan of Heian-kyō in jō (c. 3 m): the width of every avenue and street, the 40-jō square of the block (machi), and the overall dimensions of the city.
Emperor Daigo ordered the compilation in 905; it was presented in 927 and put in force in 967. Most of its fifty books are rules for the rites of the gods and for the daily working of each office: quantities of offerings, schedules of duties, forms of documents. Because they describe what officials actually did, they are the best single source for the government and material life of the Heian court.
The offices of the Left (eastern) and Right (western) Capital governed the two halves of the city on either side of Suzaku-ōji. Their regulations include a table of the capital’s measurements (kyōtei): 1,508 jō from east to west and 1,753 from north to south; Suzaku-ōji 28 jō wide; the avenues (ōji) 8 to 12 jō, and Nijō-ōji before the palace 17; the lanes (kōji) 4 jō; and each block 40 jō square, sixteen of them making a ward (bō). The East and West Markets and their offices are regulated in the same part of the book.
The book, part by part
I Book 42: the Offices of the Left and Right Capital and the markets
The measurements of Heian-kyō: blocks, wards, avenues and lanes; the administration of the two halves of the city and of the East and West Markets.
Rules: The jōbō grid: blocks of forty jō · The palace at the north, the city to its left and right