Strong and Loyal Army

Severus was a strong and able ruler.
The Roman Empire reached its greatest extent under his reign—over 5 million square kilometers.
He adopted the policy of better-paid army and was criticized by his contemporaries due to increase in tax burden on civilian population.
Later, the large military expenditure caused problems for all of his successors.

Debasement of Currency

To maintain his enlarged military, he debased the Roman currency.
Upon his accession he decreased the silver purity of the denarius from 81.5% to 78.5%.
Nevertheless, the following year he debased the denarius again because of rising military expenditures.
By 196CE, silver purity decreased from 78.5% to 54%—the silver weight dropping from 2.46 grams to 1.82 grams.
Severus’ currency debasement was the largest since the reign of Nero, compromising the long-term strength of the economy.

Victory over Parthian Empire

His legions sacked the Parthian royal city of Ctesiphon and he annexed the northern half of Mesopotamia to the empire. Later, Severus took the title Parthicus Maximus
His victory over the Parthian Empire was for a time decisive, securing Nisibis and Singara for the empire and establishing a status quo of Roman dominance in the region until 251.

Construction & Development

Severus was also distinguished for his buildings. Apart from the triumphal arch in the Roman Forum carrying his full name, he also built the Septizodium in Rome.
He enriched his native city of Leptis Magna, including commissioning a triumphal arch on the occasion of his visit of 203.
His enlargement of the Limes Tripolitanus region secured Africa and increased the agricultural base of the empire where he was born.