Dusk begins to fall as Khartoum's street vendors throw open their stalls bulging with stacks of vegetables, fruits, and spices. Smoke hangs low over the ubiquitous kebab stands.
Turbaned nomads from the north, light-skinned merchants from the Red Sea, and black tribesmen from the Nile in the south -- all mingle in the narrow market alleyways and contribute to the din of Arabic, English, and other languages spoken here.
The market gathering only hints at the cultural and ethnic diversity of Sudan.
About 3 1/2 times the size of Texas, this country stretches more than 1,000 miles from the barren deserts of the north to the mountains and rain forests of the south. Dozens of languages are spoken by as many ethnic groups. Muslims dominate the north. The south is animist and Christian.
Sudan is faced with an intriguing but hazardous challenge: how to be a united nation and a corridor between the cultures of the Arab and African worlds.
It is difficult for the Sudanese to behave in a united way. Prospects of secession in the south have begun to simmer - again.
President Jaafar Nimeiry has worked hard to reconcile differences since the end of Sudan's 17-year civil war in 1977. But an Islamic revival in the north appears to be pressuring him into favoring Muslim dominion even more.
His handling of the country's downhill economy and his plans to divide the south into three smaller regions are bitterly resented by many southerners. Southerners consider his plan to divide their region as reneging on grants of limited autonomy in the 1972 Addis Ababa agreement. It is also viewed as a tactic to weaken political opposition.
Western diplomats say Nimeiry is swayed by political motivation but that decentralization also makes economic sense:
''The south is simply too big a region to be run on its own,'' notes one observer. Unfortunately, it comes at a very inopportune moment. The country has enough problems already.
The south suffers from economic neglect and has good reason to feel suspicious:
''In many respects, it is a bit like Northern Ireland between the Catholics and Protestants,'' says a European aid official. Physically, culturally, and ethnically, the south all too often emerges as an area totally removed from the north.
One of Nimeiry's biggest mistakes has been his failure to develop road, river , and air transport between the two regions. Communications are unreliable.
Last summer, there were no flights between Khartoum and the south for nearly two months.Passengers wishing to visit the capital had to travel via Nairobi.
''This shows lack of foresight in trying to keep the two parts together,'' says a French businessman in Khartoum. ''The southerners see this as just another example of northern discrimination.''
There are over 1,000 languages and dialects in Sudan, but Arabic, the official language, is gradually asserting itself in the south and pushing out English as the lingua franca. This has aroused considerable bitterness among the southern educated elite. So has the government policy of building new mosques and plans to introduce the Sharia or Islamic law below the ''Arab belt.''
At the same time, however, one is struck by the conscientious attempts by some northerners and southerners to overcome such problems:
''It may take a generation or two,'' said a Western-educated Sudanese official from Juba in the south. ''But if our experiment works, Sudan will have an important role to play in bringing Africa and the Middle East together.''
Such is the geopolitical importance of Sudan. Nimeiry has established himself a reputation as a stabilizer between the two worlds. Yet some observers feel he has jeopardized his position by moving too quickly to embrace the West. He is also walking a political tightrope with his attempts to reconcile the fundamentalist Muslim Brotherhood and the opposition group led by Sadiq el-Mahdi known as the Mahdist movement.
There is much dissatisfaction with his policies, particularly his tendency to change political direction at the drop of a hat. Islamic revivalists are notably displeased with Nimeiry's steadfast support of the Camp David accords.
He has been criticized by the Arabs, who carry substantial economic weight in Sudanese affairs through their investment and through employment of Sudanese nationals in the Gulf. Nimeiry has done much to appease the Arabs, but for the moment he regards the United States and Western Europe as the most effective partners to bring Sudan out of its economic doldrums and to provide political stability.
Alleged Libyan subversion remains a concern. The presence of the African peacekeeping force in Chad has averted cross-border military aggression by Col. Muammar Qaddafi. So has US military support and Egyptian President Hosni Mubarak's ability to assert control in his country.
Nimeiry still distrusts Chad leader Goukhouni Woddei and has made no apparent move to restrain the rebel forces of Hissein Habre from operating along Sudan's western borders with Chad. There is the nagging feeling that unless the Organization of African Unity can maintain peace, Libya might move back to counter Habre's recent military gains.
''Nimeiry harbors an emotional hatred for Qaddafi -- a mutual one, I might add - and has a tendency to see the hand of Libya and Moscow everywhere,'' says a senior European diplomat.
There is the constant fear that the Libyans might step up their backing of some of the Islamic opposition troops as well as unreconciled southerners based in Ethiopia. Repeated Libyan-backed Mahdist-Muslim Brotherhood coup attempts in the past year have raised President Nimeiry's suspicion.
The Aden friendship and cooperation treaty signed last August by Libya, South Yemen, and Ethiopia -- all of which have close links with the Soviet Union -- is regarded as yet another Qaddafi tactic to spread his influence in the Middle East and establish a foothold in the Horn of Africa.