The Sphinxes Gate shows two sphinxes with obvious Egyptian influence. They wear wigs with hair reaching to their shoulders. They date from the 1600-1200 BC Great Hittite Empire, when nearby Hattusha (Bogazkale, see the gallery) was the capital. The city had another gate, of which only the foundations have been found.
Here you see details of the relief's on the inside of the gate. It's a double headed eagle, a motive that's very ancient and is present also at the Assyrian colony at Kanesch (Kültepe). The animals in its / their (?) claws are probably hares.