If by ‘Roman fighting techniques’ you mean the famous Testudo formation, then the answer is no, not that we know of. At least not after the collapse of the Western Roman Empire. Apart from the Testudo, there is very little in terms of fighting technique, excluding things like the actual organisation of Roman units, that is entirely unique to the Romans.

As for the shield wall, that is a broad style of fighting that developed independently in many different cultures. The Greek phalanx is an example of a shield wall, as is the Roman style which developed out of the phalanx. The shield wall as used by the Vikings was the primary fighting formation of the Scandinavian peoples of Norway, Sweden and Denmark. It was also, however, the primary fighting formation of the Saxons, Angles and Jutes, as well as many other Germanic peoples such as the Franks. So any depiction, as seems to be the case in certain parts from what I’ve seen of the Last Kingdom tv series (but not the books I might add), that has the Vikings fighting in a shield wall and the Anglo-Saxons not doing the same is inaccurate.

I should also note that the Germanic form of shield wall involved the front rank interlocking shields to create a literal wall of shields. Only the front rank was involved. The ranks behind did not lift their shields up above to make the wall higher.

So entrenched was the shield wall in Germanic/Nordic warfare that it was to the exclusion of cavalry. Wealthy Anglo-Saxons, for example, would ride to the battlefield but dismount for the actual fighting. At the Battle of Hastings in 1066, King Harold fielded no cavalry.

The independent development of the shield wall is a testament to its general effectiveness as a battlefield formation. Indeed, in Northern Europe the only way to break an enemy shield wall, excluding sheer attrition, was a flying wedge formation, known in Norse as Svinfylking (‘boar’s snout’) and among the Germanic peoples as Schweinskopf (‘swine’s head’). This was a large wedge formation that possessed the momentum to penetrate an enemy shield wall at the point of the wedge and drive through, widening the gap.