Air carrier Captain reported that the aircraft rolled back approaching the stop point at the gate due to up hill slope. Taxi continued until aircraft taxied over chocks. Aircraft was then towed in.

Narrative

When taxiing into ZZZ Gate XX; the marshaller indicated we had very little distance left to roll by having the taxi wands held vertically and close together as if to indicate the X" at any second. As I slowed down; we actually stopped short and rolled slightly back a few inches as it's an "up hill" taxi into that gate. As I applied power to taxi forward; the marshaller gave the "X" signal to stop almost immediately after I started to move forward again and as as I did we felt a mild thump just before setting the parking break. The ground crew contacted me via the inter-phone and said I taxied over a nose chock and we'd need a tug to hook up and move us clear of the chock which was stuck somehow in the nose gear. After we were properly parked; I went down to the ramp to have the supervisor explain to me what had happened. Apparently a ramp person placed a chock directory in front of the gear instead of off to the side. I saw no apparent damage however I reported the incident to Maintenance Control in case there was/is any maintenance procedure for this type sort of thing."