In verse 18, it was said: وَجَعَلْنَا بَيْنَهُمْ وَبَيْنَ الْقُرَى الَّتِي بَارَكْنَا فِيهَا قُرًى ظَاهِرَةً وَقَدَّرْنَا فِيهَا السَّيْرَ سِيرُوا (And We had made towns to be seen between them and between the towns in which We had placed Our blessings, and had measured the journey between them: "Travel along them at nights and days peacefully. - 18" ) This verse mentions yet another blessing Allah Ta’ ala had bestowed on the people of Saba'. Then it goes on to refer to the ungratefulness of those people who acted ignorantly and chose to ask for a reversal of this blessing by praying that the thing be made harder and more challenging for them. The statement: الْقُرَى الَّتِي بَارَكْنَا فِيهَا (towns in which We had placed Our blessings) in this verse probably means the rural areas of the country of Syria, because the reference to the descent of mercy in several verses of the Qur'an is specifically related to that country. The sense of the verse is that Allah Ta’ ala had made their travels to the towns of Syria very easy for them during their trips they had to undertake for their business. Given the conditions that prevailed in the world of that time, the travel distance between the city of Ma'arib and the country of Syria was fairly long with routes being uneven. In view of this difficulty, Allah Ta’ ala had blessed the people of Saba' by having made for their convenience a series of towns at intermittent distances all the way from the city of Ma'arib to the country of Syria.
These habitations were close by the main road, therefore, these were called: قَدَّرْنَا فِيهَا السَّيْرَ (had measured the journey between them). These habitations appearing one after the other were a source of convenience for weary travelers. If a traveler from one of them left home in the morning, he had the choice of reaching some other town on his way, stop there, have lunch or take rest as he wished and could leave after Zuhr and reach the next stage by sundown and spend the night there. The sentence: سِيرُوا فِيهَا لَيَالِيَ وَأَيَّامًا آمِنِينَ (Travel along them at nights and days peacefully - 18) means that these habitations were made at distances that were balanced and equal so that they would reach from one to the other within a fixed time.
In the last sentence of verse 18: (Travel along them at nights and days peacefully.), mention has been made of a third blessing bestowed on the people of Saba'. It means that these settlements were located at such equal and balanced distances that a traveler would be able to cover them in almost identical time. Then the routes were secure. Theft and highway robbery were unknown. One could travel at any time of the night or day without any hesitation or concern.