Under Gerlach II, the city of Limburg an der Lahn achieved its highest medieval flowering.
The chronicler Tilemann Elhen reported that, at the height of its prosperity, the city could summon over 2,000 weapons-capable citizens.
In 1331 Gerlach joined the Landfriedensbündnis (country peace alliance) of the Archbishop of Trier, Baldwin of Luxembourg.
The city of Limburg was strategically important due to its location on the main trade route from Cologne to Frankfurt.
This led to frequent conflicts with neighbouring lordships and made the city a target of robber barons.
The suburbs of Limburg extended beyond the limits of his dominion, leading to regular disputes with the neighboring Counts of Diez.
Under Gerlach’s administration, numerous construction projects, some of them started by his father, were completed in Limburg.
He allowed the Williamite monastery founded on the island in the Lahn in 1312 to relocate in 1317 to a new building in the suburb in front of the Diez Gate.
In the same year, in response to a request by Gerlach, Louis' rival, King Charles IV, authorized the City of Limburg to collect bridge tolls.
Reinhard I of Westerburg, a supporter of Ludwig, had captured Grenzau Castle from Trier and on April 20, 1347, a relief army sent by Baldwin attacked from the rear.
On the day of judgment, about 800 soldiers from Westerburg were in Dietkirchen, while the army of Trier made its camp near Diez.