Kastane is a short curved single-edged sword

Sword

A sword is a bladed weapon used primarily for cutting or thrusting. The precise definition of the term varies with the historical epoch or the geographical region under consideration...

 of Sri Lanka.
Kastanes often have elaborate hilts, especially shaped as lion heads.
They first arise in the Kandyan Kingdom (16th century), likely inspired by the Portuguese period in Ceylon

Portuguese period in Ceylon

Portuguese Ceylon was a Portuguese territory in present-day Sri Lanka, representing a period in Sri Lankan history from 1505–1658. The Portuguese first encountered the Ceylonese kingdom of Kotte, with whom they signed a treaty. Portuguese Ceylon was established through the occupation of Kotte and...

 and as such in origin imitations of European Renaissance weapons.

This type of sword is displayed in the modern Flag of Sri Lanka

Flag of Sri Lanka

The flag of Sri Lanka, also called the Lion Flag, consists of a gold lion, holding a kastane sword in its right fore paw, in front of a crimson background with four golden bo leaves, one in each corner. Around the background is a yellow border, and to its left are 2 vertical stripes of equal size...

 and are used by general officers of the Sri Lanka Army.