Chashtana (Greek: Ϲιαϲτανϲας Siastansas (epigraphic), Τιαστανης Tiastanēs; Brahmi: Ca-ṣṭa-na Caṣṭana; Kharosthi: 𐨖𐨛𐨞 Cha-ṭha-ṇa, Chaṭhaṇa), also known as Tisman Ror was a Kardamaka dynasty ruler of the Saka Western Satraps in northwestern India during 78-130 CE, when he was the satrap of Ujjain. He was a descendant of Kardhaman, son of Raja Dhaj and son of Ysamotika.

Chashtana's name is attested in the Greek forms Siastansas (Ϲιαϲτανϲας) and Tiastanēs (Τιαστανης), in the Brahmi form Caṣṭana () and the Kharosthi form Chaṭhaṇa (𐨖𐨛𐨞), which are derived from the Saka name *Caṣṭana, meaning "master".

Among modern scholars, the beginning of the Saka era is widely equated to the ascension of Chashtana (possibly to Mahakshatrapa) in 78 CE.

A statue found in Mathura together with statues of the Kushan king Kanishka and Vima Taktu, and bearing the name "Shastana" (Middle Brahmi script of the Kushan period: Ṣa-sta-na) is often attributed to Chashtana himself. Chashtana is called Tisman by the bards, a spelling that matches the Greek rendition of his name more closely.

Chashtana was mentioned by Ptolemy as Tiastanēs, ruling a large area of Western India into the 2nd century CE, especially the area of Ujjain ("Ozene"), during the reign of the Satavahana king Vasisthiputra Sri Pulamavi. According to Ptolemy, Chashtana directly ruled Ujjain, while Paithan (Pratisthana) continued to be ruled by Siristolemaios (identified with Sri Pulumayi, son of Gautamiputra Satakarni). Ptolemy in his "Geographia", where he classifies the Western Satraps as "Indo-Scythians", describes Chashtana's territory as starting from Patalene in the West, to his capital Ujjain in the east ("Ozena-Regia Tiastani", "Ozene, capital of king Chashtana"), and beyond Barigaza in the south:

Moreover the region which is next to the western part of India, is called Indoscythia. A part of this region around the (Indus) river mouth is Patalena, above which is Abiria. That which is about the mouth of the Indus and the Canthicolpus bay is called Syrastrena. (...) In the island formed by this river are the cities Pantala, Barbaria. (...) The Larica region of Indoscythia is located eastward from the swamp near the sea, in which on the west of the Namadus river is the interior city of Barygaza emporium. On the east side of the river (...) Ozena-Regia Tiastani (...) Minagara".

— Ptolemy Geographia, Book Seven, Chapter I

Chashtana was the grandfather of the great Western Satrap conqueror Rudradaman I. Chashtana was founder of one of the two major Saka Satrap dynasties in north-western India, the Kardamaka (Bhadramukhas); the other, short-lived dynasty, the Kshaharatas ("Satraps"), included Bhumaka and Nahapana.