Looking at the citations from OED (see below), I'm guessing this was already, or was fast becoming, an archaism. OED † Mart, n.1 Forms: OE–ME Marte, ME–16 Mart. (Show Less) Etymology: < classical Latin Mārt-, Mārs (see Mars n.1). Compare Mars n.1(Show Less) Obs. 1. a. Mythol. (The name of) Mars, the ancient Roman god of war. OE Prognostics (Tiber.) in Archiv f. das Studium der Neueren Sprachen (1908) 120 297 Si fuerit kalendas Januarius die Martis, hiems nobilissima, uer uentuosus, [etc.] : Gif bið dæg martes winter æþelust lænten wind-hladen [etc.]. OE Byrhtferð Enchiridion (Ashm.) ii. iii. 118 Þæs Sunnandæges nama wæs of þære sunnan, and þæs Monandæges of þ[am] monan, and Tiwesdæges of Marte Iouis sunu. c1385 Chaucer Knight's Tale 2024 Ther were also of Martes deuyssioun The barbour and the bochier and the smyth. a1425 (1385) Chaucer Troilus & Criseyde (1987) ii. 988 Al esily, now, for the love of Marte‥for every thing hath tyme. c1450 (1380) Chaucer House of Fame 1446 Yren Martes metal ys, Which that god is of bataylle. a1525 (1513) W. Dunbar Ballat Abbot of Tungland (Asloan) in Poems (1998) 58 Sum held he had bene Dedalus,‥Sum Martis blaksmyth Wlcanus. 1590 Spenser Faerie Queene i. Introd. iii, Triumphant Mart, In loves and gentle jollities arraid. OE—1590(Hide quotations) Thesaurus » Categories » b. Also as mart. War, battle. Freq. in in equal mart [after classical Latin aequo Mārte, ablative singular (Caesar Gallic War 7.19.3)] : in a fair contest, on equal terms. ?a1475 (1425) tr. R. Higden Polychron. (Harl.) (1869) II. 149 The Scottes‥toke to theyme seetes, what thro marte other fauor, nye to the Pictes. a1522 G. Douglas in tr. Virgil Æneid (1957) i. Prol. 516 The horrible sterne dedis of Mart. 1567 G. Turberville tr. Ovid Heroycall Epist. 45v, But if thou long for warre, or yong Iulus seeke By manly Mart to Purchase prayse and giue his foes the gleeke. 1600 E. Fairfax tr. Tasso Godfrey of Bulloigne vi. xxxvi. 100 These fooles thus vnder foot I tread, That dare contend with me in equall mart. a1640 P. Massinger Bashful Lover ii. viii. 71 My father (on whose face he durst not look In equal mart). ?a1475—a1640(Hide quotations) Thesaurus » Categories » 2. (The name of) the planet Mars. [OE Byrhtferð Enchiridion (Ashm.) i. i. 4 Þurh þæne [circul] yrnð seo sunne and se mona and þas steorran Saturnus and Iouis, Martis and Veneris and Mercurius.] c1385 Chaucer Knight's Tale 2021 Yet saugh I brent the shippes hoppesteres, The hunte strangled with the wilde beres‥Naught was forgeten by the infortune of Marte. a1393 Gower Confessio Amantis (Fairf.) vii. 1360 Complexion he takth of Marte. c1385—a1393(Hide quotations) Mart, n./1 Third edition, July 2010; online version November 2010. <http://www.oed.com:80/Entry/114406>; accessed 23 January 2011. An entry for this word was first included in New English Dictionary, 1905. -- Dr. David Wilson-Okamura http://virgil.org [log in to unmask] English Department Virgil reception, discussion, documents, &c East Carolina University Sparsa et neglecta coegi. -- Claude Fauchet