Buenos Aires, a city and port of Argentina, and capital of the republic, in 34° 36′ 21′ S. lat. and 58° 21′ 33′ W. long., on the west shore of the La Plata estuary, about 155 m. above its mouth, and 127 m. W. by N. from Montevideo. The estuary at this point is 34 m. wide, and so shallow that vessels can enter the docks only through artificial channels kept open by constant dredging. Previously to the construction of the new port, ocean-going vessels of over 15 ft. draught were compelled to anchor in the outer roads some 12 m. from the city, and communication with the shore was effected by means of steam tenders and small boats, connecting with long landing piers, or with carts driven out from the beach. The city is built upon an open grassy plain extending inland from the banks of the estuary, and north from the Riachuelo or Matanzas river where the "Boca" port is located. Its average elevation is about 65 ft. above sea-level. The federal district, which includes the city and its suburbs and covers an area of 72 sq. m., was detached from the province of Buenos Aires by an act of congress in 1880. With the construction of the new port and reclamation of considerable areas of the shallow water frontage, the area of the city has been greatly extended below the line of the original estuary banks.

The streets of the old city, which are narrow and laid out to enclose rectangular blocks of uniform size, run nearly parallel with the cardinal points of the compass, but this plan is not closely followed in the new additions and suburbs. This uniformity in plan, combined with the level ground and the style of buildings first erected, gave to the city an extremely monotonous and uninteresting appearance, but with its growth in wealth and population, greater diversity and better taste in architecture have resulted.

The prevailing style of domestic architecture is that introduced from Spain and used throughout all the Spanish colonies - the grouping of one-storey buildings round one or two patios, which open on the street through a wide doorway. These residences have heavily barred windows on the street, and flat roofs with parapets admirably adapted for defence. The domiciliation of wealthy foreigners, and the introduction of foreign customs and foreign culture, have gradually modified the style of architecture, both public and domestic, and modern Buenos Aires is adorned with many costly and attractive public edifices and residences. French renaissance, lavishly decorated, has become the prevailing style. The Avenida Alvear is particularly noted for the elegance of its private residences, and the new Avenida de Mayo for its display of elaborately ornamented public and business edifices, while the suburban districts of Belgrano and Flores are distinguished for the attractiveness of their country-houses and gardens.

A part of the population is greatly overcrowded, one-fifth living in conventillos, or tenement-houses.

Among the city's many plazas, or squares, twelve are especially worthy of mention, viz.: 25 de Mayo (formerly Victoria) on which face the Government-House and Cathedral, San Martin (or Retiro), Lavalle, Libertad, Lorea, Belgrano, 6 de Junio, Once de Setiembre, Independencia (formerly Conceptión), Constitución, Caridad and 29 de Deciembre. These vary in size from one to three squares, or 4 to 12 acres each, and are handsomely laid out with flowers, shrubbery, walks and shade trees. There are also two elaborately laid out alamedas, the Recoleta and the Paseo de Julio, the latter on the river front and partially absorbed by the new port works, and the great park at Palermo, officially called 3 de Febrero, which contains 840 acres, beautifully laid out in drives, footpaths, lawns, gardens and artificial lakes. In all, the plazas and parks of Buenos Aires cover an area of 960 acres.

The cathedral, which is one of the largest in South America, dating from 1752, resembles the Madeleine of Paris in design, and its classical portico facing the Plaza 25 de Mayo has twelve stately Corinthian columns supporting an elaborately sculptured pediment. The archbishop's palace (Buenos Aires became an archiepiscopal see in 1866) adjoins the cathedral. There are about twenty-five Roman Catholic churches in the city, one of the richest and most popular of which is the Merced on Calle Reconquista, and four Protestant churches - English, Scottish Presbyterian, American Methodist and German Lutheran. Twenty asylums for orphans and indigent persons and one for lunatics are maintained at public expense and by private religious associations, while the demand for organized medical and surgical treatment is met by fifteen well-appointed hospitals, having an aggregate of 2600 beds, and treating 17,000 patients annually. Of these, five belong to foreign nationalities. The city has six cemeteries covering 230 acres.

Among the more noteworthy public buildings are the Casa Rosada (government-house), facing the Plaza 25 de Mayo and occupying in part the site of the fort built by Garay in 1580; the new congress hall on Calle Callao and Avenida de Mayo, finished in 1906 at a cost of about £1,300,000; the new municipal hall on Avenida de Mayo; the bolsa or exchange, distributing reservoir, mint, and some of the more modern educational buildings. Higher education is represented by the university of Buenos Aires, with its several faculties, including law and medicine, and 3562 students (1901), four national colleges, three normal schools and various technical schools. There are, also, a national library, a national museum, a zoological garden and an aquarium. The people are fond of music, the drama and amusements, and devote much time and expense to diversions of a widely varied character, from Italian opera to horse-racing and pelota. They have two or three large public baths, and a large number of social, sporting and athletic clubs. The Porteños, as the residents of Buenos Aires are called, are accustomed to call their city the "Paris of America," and not without reason.

Buenos Aires has become the principal manufacturing centre of the republic, and its industrial establishments are numbered by thousands and their capital by hundreds of millions of dollars.

The growth of Buenos Aires since settled conditions have prevailed, and especially since its federalization, has been very rapid, and the city has finally outstripped all rivals and become the largest city of South America. At the time of its first authentic census in 1869, it had a population of 177,767. In 1887, when the suburbs of Belgrano and Flores with an aggregate population of 28,000 were annexed, its population without this increment was estimated at 404,000. In 1895 the national census gave the population as 663,854, and in 1904 a municipal census increased it to 950,891. At the close of 1905 the national statistical office estimated it at 1,025,653. The excess of births over deaths is unusually large (about 14 per thousand in 1905). The city has about one-fifth of the population of the whole republic. The government is vested in an intendente municipal (mayor) appointed by the national executive with the approval of the senate, and a concejo deliberante (legislative council) elected by the people and composed of two councillors from each parish. The police force is a military organization under the control of the national executive, and the higher municipal courts are subject to the same authority.

Every ratepayer, whether foreigner or native, has the right to vote in municipal elections and to serve in the municipal council.

The water-supply is drawn from the estuary at Belgrano and conducted 3½ m. to the Recoleta, where three great settling basins, with an aggregate capacity of 12,000,000 gallons, and six acres of covered filters, are located. It is then pumped to the great distributing reservoir at Calles Córdoba and Viamonte, which covers four acres and has a capacity of 13,500,000 gallons. These works were begun in 1873. Up to 1873, when the water and drainage works were initiated by English engineers and contractors, there were no public sewers, and the sanitary state of the city was indescribably bad. The cholera epidemic of 1867-1868, with 15,000 victims, and the yellow fever epidemic of 1871, with 26,000 victims, were greatly intensified by these insanitary conditions. The construction of the sewers lasted about 19 years, when in 1892 the water and drainage works were taken over by the government, and are now administered at public expense and at a profit. The main sewer is 16 m. long and extends southward beyond Quilmes. The total cost of the two systems exceeded six millions sterling.

Buenos Aires is now provided with a good water-supply, and its sanitary condition compares favourably with that of other great cities, the annual death-rate being about 18 per thousand, against 27 per thousand in 1887. Its mean annual temperature is 64° Fahr., and its annual rainfall 34 in.

The lighting includes both gas and electricity, the former dating from 1856. Previously to that time street lighting had been effected at first with lamps burning mares' grease, and then with tallow candles. The streets were at first paved with cobble-stones, then with dressed granite paving-stones (parallelepipedons), and finally with wood and asphalt. The tram service is in the hands of nine private companies, operating 313 m. of track (31st of December 1905), on almost five-sevenths of which electric traction is employed. The city is the principal terminus and port for nearly all the trunk railway lines of the republic, which have large passenger stations at the Retiro, Once de Setiembre, and Constitución plazas, and are connected with the central produce market and the new Madero port. The great central produce market at Barracas al Sud (Mercado Central de Frutos), whose lands, buildings, railway sidings, machinery and mole cost £750,000, is designed to handle the pastoral and agricultural products of the country on a large scale, while 20 markets in the city meet the needs of local consumers.

The most important feature of the port of Buenos Aires is the "Madero docks," constructed to enlarge and improve its shipping facilities. Improvements had been, begun in 1872 at the "Boca," as the port on the Riachuelo is called, and nearly £1,500,000 was spent there in landing facilities and dredging a channel 12 m. in length, to deep water. These improvements were found insufficient, and in 1887 work was begun on plans executed by Sir John Hawkshaw for a series of four docks and two basins in front of the city, occupying 3 m. of reclaimed shore-line, and connected with deep water by two dredged channels. The north basin is provided with two dry docks, and the new quays are equipped with 24 warehouses, hydraulic cranes, and 28 m. of railway sidings and connexions. The total cost of the new port works up to 1908 was about £8,000,000 sterling ($40,000,000 gold). In September of that year it was decided by congress to borrow £5,000,000 for still further extensions which were found to be required.

The channels to deep water require constant dredging because of the great quantity of silt deposited by the river, and on this and allied purposes an expenditure of £560,000 was voted in 1908. In 1907 there were 29,178 shipping entries in the port, with an aggregate of 13,335,737 tons, the merchandise movement being 4,360,000 tons imports and 2,900,000 tons of produce exports. The revenues for 1907 were $5,452,000 gold, and working expenses, $2,213,000 gold, the profit ($3,229,000) being equal to about 8% on the cost of construction.