According to Edward Conze, Greek Skepticism (particularly that of Pyrrho) can be compared to Buddhist philosophy, especially the Indian Madhyamika school. The Pyrrhonian Skeptics' goal of ataraxia (the state of being untroubled) is a soteriological goal similar to nirvana.
These similarities can be traced back to the origins of Pyrrhonism. Pyrrho, the founder of Pyrrhonism, spent about 18 months in Taxila as part of Alexander the Great's court during Alexander's conquest of the east. During his time in India he studied Indian philosophy and presumably encountered Early Buddhism. Centuries later, Pyrrhonism may have influenced the Buddhist philosopher Nagarjuna's Madhyamaka philosophy.
Diogenes Laërtius' biography of Pyrrho reports that Pyrrho traveled with Alexander the Great's army to India and based his philosophy on what he learned there:
...he even went as far as the Gymnosophists, in India, and the Magi. Owing to which circumstance, he seems to have taken a noble line in philosophy, introducing the doctrine of incomprehensibility, and of the necessity of suspending one's judgment....
The Pyrrhonists promote suspending judgment (epoché) about dogma (beliefs about non-evident matters) as the way to reach ataraxia. This is similar to the Buddha's refusal to answer certain metaphysical questions which he saw as non-conducive to the path of Buddhist practice and Nagarjuna's "relinquishing of all views (drsti)".
A summary of Pyrrho's philosophy was preserved by Eusebius in Praeparatio evangelica, quoting Aristocles, quoting the Pyrrhonist philosopher Timon, quoting his teacher, Pyrrho, in what is known as the "Aristocles passage."
"Whoever wants to live well (eudaimonia) must consider these three questions: First, how are pragmata (ethical matters, affairs, topics) by nature? Secondly, what attitude should we adopt towards them? Thirdly, what will be the outcome for those who have this attitude?" Pyrrho's answer is that "As for pragmata they are all adiaphora (undifferentiated by a logical differentia), astathmēta (unstable, unbalanced, not measurable), and anepikrita (unjudged, unfixed, undecidable). Therefore, neither our sense-perceptions nor our doxai (views, theories, beliefs) tell us the truth or lie; so we certainly should not rely on them. Rather, we should be adoxastoi (without views), aklineis (uninclined toward this side or that), and akradantoi (unwavering in our refusal to choose), saying about every single one that it no more is than it is not or it both is and is not or it neither is nor is not.
According to Christopher I. Beckwith's analysis of the Aristocles Passage, adiaphora (anatta), astathmēta (dukkha), and anepikrita (anicca) are strikingly similar to the Buddhist three marks of existence, indicating that Pyrrho's teaching is based on Buddhism. Beckwith contends that the 18 months Pyrrho spent in India was long enough to learn a foreign language, and that the key innovative tenets of Pyrrho's skepticism were only found in Indian philosophy at the time and not in Greece. Other scholars, such as Stephen Batchelor and Charles Goodman question Beckwith's conclusions about the degree of Buddhist influence on Pyrrho.
Conversely, while critical of Beckwith's ideas, Kuzminsky sees credibility in the hypothesis that Pyrrho was influenced by Buddhism, even if it cannot be safely ascertained:
It is now clear that Pyrrho spent months if not years in Taxila and Northwest India, at a time where Buddhists were active there. He would have had ample opportunity, it seems, to converse with local gymnosophists, whoever they may have been. That sramanas were Buddhists is a strong hypothesis, perhaps the best available. The question of direct influence cannot be confirmed with what we know now, yet we remain emboldened to historically imagine what Pyrrho might have learned from early Buddhists given his Greek background.
Ajñana, which upheld radical skepticism, may have been a more powerful influence on Pyrrho than Buddhism. The Buddhists referred to Ajñana's adherents as Amarāvikkhepikas or "eel-wrigglers", due to their refusal to commit to a single doctrine. Scholars including Barua, Jayatilleke, and Flintoff, contend that Pyrrho was influenced by, or at the very least agreed with, Indian skepticism rather than Buddhism or Jainism, based on the fact that he valued ataraxia, which can be translated as "freedom from worry". Jayatilleke, in particular, contends that Pyrrho may have been influenced by the first three schools of Ajñana, since they too valued freedom from worry.
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Because of the high degree of similarity between Madhyamaka and Pyrrhonism, particularly the surviving works of Sextus Empiricus, Thomas McEvilley and Matthew Neale suspect that Nāgārjuna was influenced by Greek Pyrrhonist texts imported into India.
According to legend, Nagarjuna said he was influenced by books inaccessible to other people. He was approached by Nagas (semi-divine serpents) in human form. They invited him to their kingdom to see some texts they thought would be of great interest to him. Nagarjuna studied those texts and brought them back to India. Matthew Neale illustrated such viewpoint inspired by Joseph G. Walser , "Nāgārjuna was a skillful diplomat concealing novel doctrines in acceptably Buddhist discourse... to conceal their doctrines’ derivation from foreign wisdom traditions." 
During this era trade between India and the Roman Empire flourished and Greek ideas became influential in India. Although there is no direct proof that Nāgārjuna had access to Greek Pyrrhonist texts, there's ample evidence of other Greek texts that were imported into India and that ideas from those texts were incorporated into Indian thought.
According to David Pingree, there is substantial similarity between ancient Indian and pre-Ptolomaic Greek astronomy. Pingree believes that these similarities suggest a Greek origin for certain aspects of Indian astronomy. One of the direct proofs for this approach is the fact quoted that many Sanskrit words related to astronomy, astrology, and calendars are either direct phonetical borrowings from the Greek language, or translations, assuming complex ideas, like the names of the days of the week which presuppose a relation between those days, planets (including Sun and Moon) and gods.
Hellenistic astronomy profoundly influenced Indian astronomy. For example, Hellenistic astronomy is known to have been practiced near India in the Greco-Bactrian city of Ai-Khanoum from the 3rd century BCE. Various sun-dials, including an equatorial sundial adjusted to the latitude of Ujjain have been found in archaeological excavations there. Numerous interactions with the Mauryan Empire, and the later expansion of the Indo-Greeks into India suggest that transmission of Greek astronomical ideas to India occurred during this period. The Greek concept of a spherical earth surrounded by the spheres of planets, further influenced the astronomers like Varahamihira and Brahmagupta.
Several Greco-Roman astrological treatises are also known to have been exported to India during the first few centuries of our era. The Yavanajataka was a Sanskrit text of the 3rd century CE on Greek horoscopy and mathematical astronomy. Rudradaman's capital at Ujjain "became the Greenwich of Indian astronomers and the Arin of the Arabic and Latin astronomical treatises; for it was he and his successors who encouraged the introduction of Greek horoscopy and astronomy into India."
Later in the 6th century, the Romaka Siddhanta ("Doctrine of the Romans"), and the Paulisa Siddhanta ("Doctrine of Paul") were considered as two of the five main astrological treatises, which were compiled by Varāhamihira in his Pañca-siddhāntikā ("Five Treatises"), a compendium of Greek, Egyptian, Roman and Indian astronomy. Varāhamihira goes on to state that "The Greeks, indeed, are foreigners, but with them this science (astronomy) is in a flourishing state." Another Indian text, the Gargi-Samhita, also similarly compliments the Yavanas (Greeks) noting that the Yavanas though barbarians must be respected as seers for their introduction of astronomy in India. For example, Numerous interactions with the Mauryan Empire, and the later expansion of the Indo-Greeks into India suggest that transmission of Greek astronomical ideas to India occurred during this period.
Catuṣkoṭi is a logical argument that is important in the Buddhist logico-epistemological traditions, particularly those of the Madhyamaka school, and in the skeptical Greek philosophy of Pyrrhonism. McEvilley argues for mutual iteration and pervasion between Pyrrhonism and Madhyamika:
An extraordinary similarity, that has long been noticed, between Pyrrhonism and Mādhyamika is the formula known in connection with Buddhism as the fourfold negation (catuṣkoṭi) and which in Pyrrhonic form might be called the fourfold indeterminacy.
In Pyrrhonism the fourfold indeterminacy is used as a maxim for practice. This maxim is also related to the shorter, "nothing more" (ou mallon) maxim used by Democritus.
McEvilley notes a correspondence between the Pyrrhonist and Madhyamaka views about truth:
Sextus says  that Pyrrhonism has two criteria regarding truth:
- [T]hat by which we judge reality and unreality, and
- [T]hat which we use as a guide in everyday life.
According to the first criterion, nothing is either true or false[.] [I]nductive statements based on direct observation of phenomena may be treated as either true or false for the purpose of making everyday practical decisions.
The distinction, as Conze has noted, is equivalent to the Madhyamika distinction between "Absolute truth" (paramārthasatya), "the knowledge of the real as it is without any distortion," and "Truth so-called" (saṃvṛti satya), "truth as conventionally believed in common parlance.
Thus in Pyrrhonism "absolute truth" corresponds to acatalepsy and "conventional truth" to phantasiai.
Buddhist philosopher Jan Westerhoff says "many of Nāgārjuna’s arguments concerning causation bear strong similarities to classical sceptical arguments as presented in the third book of Sextus Empiricus’s Outlines of Pyrrhonism."
Aulus Gellius described the Pyrrhonist view which corresponds with the Buddhist view of dependent origination as follows:
...they say that appearances, which they call φαντασίαι, are produced from all objects, not according to the nature of the objects themselves, but according to the condition of mind or body of those to whom these appearances come. Therefore they call absolutely all things that affect men's sense τὰ πρός τι (i.e., "things relative to something else.") This expression means that there is nothing at all that is self-dependent or which has its own power and nature, but that absolutely all things have "reference to something else" and seem to be such as their is appearance is while they are seen, and such as they are formed by our senses, to whom they come, not by the things themselves, from which they have proceeded.
Similarly, the ancient Anonymous Commentary on Plato's Theaetetus says, with a notable parallel with the terms from the Heart Sutra (i.e., "in emptiness there is no form, no sensation, no discrimination, no conditioning, and no awareness. There is no eye, no ear, no nose, no tongue, no body, no mind. There is no form, no sound, no smell, no taste, no texture, no phenomenon. There is no eye-element and so on up to no mind-element and also up to no element of mental awareness."):
The Pyrrhonists say that everything is relative in a different sense, according to which nothing is in itself, but everything is viewed relative to other things. Neither colour nor shape nor sound nor taste nor smells nor textures nor any other object of perception has an intrinsic character....
Suspension of belief (epoche) is the principal practice of Pyrrhonism. Nāgārjuna describes the corresponding practice in Buddhism as, “When one affirms being, there is a seizing of awful and vicious beliefs, which arise from desire and hatred, and from that contentions arise,”, “By taking any standpoint whatsoever, one is attacked by the writhing snakes of the afflictions. But those whose mind has no standpoint are not caught.”
Sextus Empiricus argued that "person" could not be precisely defined. He debunks various definitions of “human” given by philosophical schools, by showing that they are speculative and disagree with each other, that they identify properties (many not even definitive anyway) rather than the property-holder, and that none of these definitions seem to include every human and exclude every non-human. This debunking is similar to the Buddhist arguments against the existence of the “person.” The person is said to lack identifiable entity-hood. A large section of Nāgārjuna's Mūlamadhyamakakārikā is devoted to demonstrating that the experiencing person cannot be established as existing itself.
Sextus Empiricus argued that by realizing that nothing is by nature more to be striven for than avoided or vice versa, but is instead contingent on occasion and circumstances, that one can live well-spirited and untroubled, not elated (by good things because they are good) and not depressed (by evils because they are evil), and thus accepting occurrences which take place of necessity, be liberated from the distress of beliefs, be they beliefs that something bad is at hand or something good. Nāgārjuna made a nearly identical claim: “By seeing [their] lack of existence by nature, the thirst for conjoining with the good and the thirst for disjoining from difficulty are destroyed. Thus there is release.”
In the second of the Four Noble Truths, the Buddha identified desire (taṇhā) as a principal cause in the arising of dukkha (suffering, pain, unsatisfactoriness). In the Silloi Timon of Phlius said “desire is absolutely the first of all bad things” Pyrrho thought that those who dogmatize think that there is a nature of the good and the divine, and think that they can achieve “the most equable life” by acquiring that which is naturally good. Holding this belief precludes attaining ataraxia, presumably because it breeds desire.
While discussing Christopher Beckwith's claims in Greek Buddha: Pyrrho's Encounter with Early Buddhism in Central Asia, Jerker Blomqvist states that:
On the other hand, certain elements that are generally regarded as essential features of Buddhism are entirely absent from ancient Pyrrhonism/scepticism. The concepts of good and bad karma must have been an impossibility in the Pyrrhonist universe, if “things” were ἀδιάφορα, ‘without a logical self-identity’, and, consequently, could not be differentiated from each other by labels such as ‘good’ and ‘bad’ or ‘just’ and ‘unjust’. A doctrine of rebirth, reminiscent of the Buddhist one, though favored by Plato and Pythagoras, was totally alien to the Pyrrhonists. The ἀταραξία, ‘undisturbedness’, that the Pyrrhonists promised their followers, may have a superficial resemblance to the Buddhist nirvana, but ἀταραξία, unlike nirvana, did not involve a liberation from a cycle of reincarnation; rather, it was a mode of life in this world, blessed with μετριοπάθεια, ’moderation of feeling’ or ‘moderate suffering’, not with the absence of any variety of pain. Kuzminski, whom Beckwith (p. 20) hails as a precursor of his, had largely ignored the problem with this disparity between Buddhism and Pyrrhonism.
In his 2009 masters degree thesis on Pyrrhonian Skepticism and Zen Buddhism in Dialogue Carlo Jamelle Harris notes:
In light of the similarities highlighted earlier, we might be also led to ask as to how to best account for these similarities? Did the Greeks import these ideas wholesale from the Indians? Was there mutual influence or did the two systems develop independently of one another? Hinduism and Buddhism in Greek Philosophy by A. N. Marlow makes no mention of either Pyrrho or Skepticism, but gives a good overview of the influence of Indian thinking on the Greeks, which no doubt account for some of the overall affinities in thought between the two civilizations. Everard Flintoff’s Pyrrho and India is also notable for its explorations of the Indian influence in Pyrrho’s thought, though its findings appear in my opinion mostly speculative. And Adrian Kuzminski, in his Pyrrhonism: How the Ancient Greeks Reinvented Buddhism, follows up on the work of Flintoff though without coming to any firm conclusions while making the case, unsuccessfully I think, of an unbroken line of thought from Pyrrho to Sextus Empiricus. In any case, the Skeptics never affirm any Buddhist- or Indian-sounding concepts such as reincarnation, other worlds, karma, or even meditation (the absence of meditation in the Greek Skeptical tradition appears to weaken the case for Indian influence, as Kaziminski notes albeit somewhat indirectly). Pyrrhonian Skepticism seems thus rooted more or less in epistemological concerns important to the Greeks and it never engages in any soteriological discourse (in any other-worldly sense) and seeks no form of escape from the body or world, but from disturbance-causing beliefs, a trait that is also characteristic of the advanced stages of Zen Buddhist practice.
Varāhamihira's knowledge of Western astronomy was thorough. In five sections, his monumental work progresses through native Indian astronomy and culminates in two treatises on Western astronomy, showing calculations based on Greek and Alexandrian reckoning and even giving complete Ptolemaic mathematical charts and tables.