Roman engineering skills allowed the strengthening of the empire in many ways, including, but not limited too:
1) Roads: Building roads made of smoothed stone allowed faster traveling, as (even seen today), people travel better on solid surfaces than on ground.
2) Bridges: While Romans did not invent bridges, they were able to make better bridges that lasted through the centuries
3) Aqueducts: One of the largest and best feats the Romans were able to create, bringing water from hundreds to thousands of miles away to cities, which allowed the growth of the empire.
4) Heavy artillery machinery: Not the kind of artillery you usually think of, the Romans were able to build catapults, armored rams, and other tools to help them conquer others.
etc.
hope this helps