Umar stood for simplicity and austerity. Consequently he did not believe in any large scale programme of public works involving extravagance. Nevertheless as a consequence of the extension of the Muslim rule to distant lands, the undertaking of works of public utility became imperative.
As Muslim conquests extended east and west, and more people embraced Islam, it became necessary to construct mosques. The mosques were not mere places for offering prayers; these were community centres as well where the faithful gathered to discuss problems of social and cultural importance. During the caliphate of Umar as many as four thousand mosques were constructed extending from Persia in the east to Egypt in the west Umar enlarged and improved the Prophet's mosque in Madina. He also paved the Holy Kaaba.
During the caliphate of Umar many new cities were founded. These included Kufa, Basra, and Fustat. These cities were laid in according with the principles of town planning. All streets in these cities led to the Friday mosque which was sited in the central chauk. Markets were established at convenient points. The cities were divided into quarters, and each quarter was reserved for particular tribes. In the construction of houses, strict instructions were laid down prohibiting the construction of palatial buildings. The houses were to be single storeyed, not exceeding specified dimensions. These instructions were vigorously enforced, and if any body constructed a double storey in violation of these instructions, such double storeys were invariably demolished. The houses did not reflect the opulence or poverty of the owners. These were symbolic of the egalatarian society of Islam, whereunder all were equal.
Many buildings were built for administrative purposes. In the quarters called "Dar-ul-Amarat" Government offices and houses for the residence of officers were provided. Buildings known as 'Diwans' were constructed for the keeping of official records. Buildings known as Bait-ul-Mal, were constructed to house public treasuries. For the lodging of persons suffering sentences as punishment, prison houses were constructed for the first time in Muslim history. In important cities Guest Houses were constructed to serve as rest houses. Roads and bridges were constructed for public use. On the road from Madina to Mecca, shelters, wells, and meal houses were constructed at every stage.
Military cantonments were constructed at strategic points. Special stables were provided for cavalry. These stables could accommodate as many as 4,000 horses. Special pasture grounds were provided and maintained for Bait-ul-Mal animals.
Canals were dug to irrigate fields as well as provide drinking water for the people. Abu Musa Canal was a nine mile long, canal which brought water from the Tigris to Basra. Another canal known as Maqal canal was also dug from the Tigris. A canal known as the Amirul Mumnin canal was dug to join the Nile to the Red Sea. During the famine of 639 A.D. foodgrains were brought from Egypt to Madina through this canal and the sea. Saad canal dug from the Euphrates brought water to Anbar. Amr bin Al Aas the Governor of Egypt even proposed the digging of a canal to join the Mediterranean to Red Sea. The proposal, however, did not materialise, and it was 1200 years later that such a canal was dug in the shape of the Suez Canal.