Read this amazing wiki entry on the Roman military engineering expertise.
Way far ahead of Roman contemporaries??!! Was a very institutionalized, integral, and important aspect of the Roman legion and Roman military conquest.
My comments on the wiki entry [in BOLD as usual!!]"
"The military engineering of Ancient Rome's armed forces was of a scale and frequency far beyond that of any of its contemporaries . . . each Roman legionary had as part of his equipment a shovel"
The Romans were hardly the first to employ military engineers, but it was the scale, and institutionalized aspect of their engineering that made them unique in this respect.
"when on the march, particularly in enemy territory, the legion would, after a day's marching, construct a fortified camp or castra, requiring as raw materials only earth, turf and timber . . . A legion could throw up a camp under enemy attack in as little as a few hours."
We have to be clear here. EACH AND EVERY DAY DURING THE MARCH OF A LEGION, A NEW CAMP WOULD BE CONSTRUCTED. A FORTIFIED CAMP, COMPLETE WITH MOAT [A DITCH BY MODERN PARLANCE, NOT WATER FILLED!] AND STOCKADE, TENTS AND INTERIOR BUILDINGS ALSO ERECTED WITHIN THE BOUNDARIES OF THE STOCKADE. EACH AND EVERY DAY WHILE ON THE MARCH - - A NEW CAMP - - FORTIFIED!!
"One of the most notable examples of military bridge-building in the Roman Empire was Julius Caesar's Bridge over the Rhine River. This bridge was completed in only ten days and is conservatively estimated to be more than 300 feet long. The construction was deliberately over-engineered for Caesar's stated purpose of impressing the Germanic tribes"
Roman roads of course required bridges! As I have said in a previous blog entry, Roman roads were generally constructed in as straight a line as possible. NOT necessarily conforming to the terrain as would be a modern road. This WAS DONE IN LARGE MEASURE FOR PSYCHOLOGICAL PURPOSES??!! The Romans are saying to the locals, "we even defy the forces of nature itself and are victorious - - what chance - - do you have against us!!??"
In World War Two [WW2], the Rhine river WAS SEEN as a major obstacle for the allied forces prior to the invasion of Germany proper. A formidable obstacle. CAPTURING THE BRIDGE AT REMAGEN WAS A MAJOR COUP DE MAIN OF SIGNIFICANT PROPORTIONS!! The British Army when crossing the Rhine  did so only with an effort that in magnitude closely resembled the Normandy invasion [D-Day].
In his book, "The Liberators", Suvorov speaks of Operation 'Bridge'. The construction of a railroad bridge designed to impress foreign observers!! The Soviets were trying to say, "even the Rhine is not an obstacle to us!!" Big Red moving from east to west will NOT be stopped by an insignificant obstacle as the Rhine. NATO BEWARE!!
[the bridge was a sham, according to Suvorov, but must have been impressive to some. I recall seeing a U.S. Army booklet from the era of the Cold War that DID describe this bridge as a "done deal"!]
[personal comment! Do you find that to be spooky? Caesar builds a great bridge across the Rhine to impress the Germanii locals. Two thousand years later the Soviets build a bridge [albeit a sham one!] to again impress the Germanii and their NATO allies!]
"The Roman army also took part in building projects for civilian use . . . the involvement of the soldiers in building works, kept them not only well accustomed to hard physical labour, but also kept them busy"
Good training. Any sergeant will tell you that. Hard physical labor, work as a team, learn skills that will be useful while on the march, etc.!!
"the scale of Roman military engineering exceeded that of any of its contemporaries in both imagination and scope."
"extra-ordinary constructions [by the Roman military engineers] . . . the walling in of the entire city of Alesia . . . within a massive length of double-wall - one inward-facing to prevent escape or offensive sallies from the city, and one outward-facing to prevent attack by Celtic reinforcements. This wall is estimated to be over 13 miles long"
That is an impressive figure. Thirteen miles. Is this the combined length of the inner and outer wall is not clear. And moat too, with watch towers, further impediments, etc.!
Romans - - can do!!