Deuteronomy 19:3

Thou shalt prepare thee a way
A road, an highway to those cities: on the first of Adar, or February, the magistrates used to meet, and proclaimed, or ordered to be proclaimed, that the ways be repaired ^F18, particularly those leading to the cities of refuge; which was done by making them smooth and plain, so that there was not an hill or dale to be seen; and by building bridges over rivers and brooks, that he might escape who had killed anyone through mistake, and not be hindered, lest the avenger of blood should overtake him and kill him ^F19; and therefore every obstruction was removed out of the way, that there might be a clear course for him; and at the parting of ways, or where two or more ways met, that he might not be at a loss one moment which way to take, "refuge" was written, as Jarchi and other writers observe, upon posts or pillars erected for that purpose: (See Gill on Numbers 35:6),

and divide the coasts of thy land, which the Lord thy God giveth thee
to inherit, in three parts;
in each of which was to be a city of refuge, and those at an equal distance: so Jarchi observes, that this was done that there might be from the beginning of the border (of the land) unto the first city of the cities of refuge, according to the measure of a journey, that there is from that to the second, and so from the second to the third, and so from the third to the other border of the land of Israel: of the situation of these cities, so as to answer to those on the other side Jordan, (See Gill on Numbers 35:14),

that every slayer may flee thither;
to that which is nearest and most convenient for him, that is, who had slain a man unawares, as follows.